Capture of the controlling positions in the Marshalls and Gilberts early in 1944 gave us command over a strategically vital area of the Pacific Ocean and permitted us to undertake the next major offensive operation, the conquest of the Marianas. These islands formed the southern end of an almost continuous chain, extending southward from Tokyo for 1,350 miles. The Nampo Shoto, the Bonins, the Volcano Islands, and the Marianas, together, provided the enemy with a series of mutually supporting airfields and bases affording him a protected line of communications from the Japanese homeland to Truk, his major Central Pacific base, and to the eastern Carolines, the Philippines, and conquered territory to the south and west. Wresting the Marianas from him would cut that important line of communication and give us bases from which we could extend our control still farther westward and on which we could base aircraft to bomb the home islands of the Empire.
Plans for the Marianas operations called for the development of large-scale facilities on the three largest island of the group -- Saipan, Tinian, and Guam. On the two northern islands, long-range bomber fields for the Army's use were to be the dominant features; Guam was to be developed both as a long-range bomber base and as the principal naval base in the Central Pacific west of Pearl Harbor.
The invasion of the Marianas was begun by an assault by the Second and Fourth Marine Divisions on Saipan on the morning of June 15, 1944. Landings were made on the southwest coast of the island, to the north and south of the town of Charan Kanoa. The Fourth Division had the capture of Aslito airfield as its objective; the Second Division's mission was the capture of Mt. Tapotchau, in the center of the island. The 121st Construction Battalion went ashore with the Fourth Division assault forces; the 18th Battalion, with the Second Division.
The landing was vigorously opposed by the Japanese defenders, and it became necessary to commit to the engagement the 27th Army Division, which was to have been held as reserve. Despite the severe fighting, Aslito airfield was in our hands by June 19, and the Seabees set about repairing the battle-damaged runway. By June 29, our fighter planes were operating from the Aslito strip, giving the front-line troops land-based air support. By July 9, Saipan was secured.
Originally, it had been intended that the capture of Tinian would follow the Saipan operation after a few days, and that the capture of Guam (by another task force) would take place shortly thereafter. The stiff defense of Saipan, however, upset this schedule. The expeditionary force reserve had to be used; furthermore, the enemy fleet made an unsuccessful attempt to contest our advance into hitherto Japanese waters [the Battle of the Philippine Sea, aka the "Marianas Turkey Shoot"]. Assaults on both Tinian and Guam were delayed, therefore, for about a month, time enough to permit bringing additional reinforcements from Hawaii.
Invasion forces landed on Guam on July 21. Possession of Apra Harbor, together with the development area surrounding it and the airfield on Orote Peninsula, was the initial objective. Landing forces struck north and south of the harbor, the Third Marine Division near Asan and the First Provisional Marine Brigade near Agat. As at Saipan, Seabees participated in the assaults -- the 25th Battalion, the 13th Special Battalion, and CBMU 515 on the southern beaches. For three weeks, combat and construction proceeded together, until August 10, when Japanese resistance came to an end.
As a development of considerable magnitude had been planned for Guam, calling for the employment of a large number of construction battalions, the 5th Construction Brigade had been formed for the purpose of coordinating and directing all construction on the island. On August 15, the brigade
assumed control of construction, and the development of base facilities for both the Army and the Navy was begun.
Guam became a great Army air base as well as the principal naval base in the western Pacific. In large measure, Army facilities were built by Army engineer troops, and Navy facilities by Seabees, but there was much interchange of construction personnel and resources, made possible by the unified construction command.
Three days after the invasion of Guam, the Fourth Marine Division moved across the narrow strait separating Saipan from Tinian. Again, the Marines were accompanied by the 18th and 121st Construction Battalions. Enemy resistance was relatively weak by this time, and the conquest of the island was quickly completed. Again, all construction was under a unified command, that of the Sixth Construction Brigade, but in this instance, naval construction battalions were made responsible for all construction, even though facilities for the Army Air Forces dominated the base-development plans. During the ensuing months, Tinian became a gigantic air base, primarily for Superfortresses engaged in the long-range bombing campaign against Japan.
By the end of 1944, the long-range strategic bombing of Japan was in full fury. The bases were 1,500 miles away from the target, however, and the B-29's had to make the entire run without fighter-plane escort or the benefit of emergency landing fields. To strengthen the attack, therefore, it became necessary to capture and develop the uninviting island of Iwo Jima, just about half way between Saipan and Tokyo.
On February 19, 1945, the assault took place. Three Marine Divisions participated -- the Third, Fourth, and Fifth -- accompanied by three construction battalions -- the 31st, 62nd, and 133rd. Resistance by the defending forces was stubborn and losses ran high, but on March 16, the island was declared secure.
Fighter fields for bomber escorts and bomber fields to serve as intermediate landing points for
Superfortresses were the principal facilities to be constructed. Fifty B-29's, returning from Japan, had made emergency landings at Iwo by the time the island was secured. The Ninth Construction Brigade was formed to control the work of the battalions made responsible for the development of Iwo.
The island, second largest of the Marianas, is about 12 miles long and 5 miles wide. Mt. Tapotchau, in the center of the island, is the dominating physical feature. Along the western shore, between Garapan and Agingan Point, there is a low and generally poorly drained coastal plain.
About 70 per cent of the island was under sugar cultivation. The population numbered about 25,000, more than 20,000 being Japanese. Garapan was the largest city and administrative center for the Saipan governmental district.
At dawn on June 15, 1944, the transports, cargo ships, and landing craft of the amphibious forces came into position off the west coast of Saipan. The Second and Fourth Marine Divisions moved in, under heavy fire from enemy mortars and small caliber guns, to establish two beachheads at the town of Charan Kanoa. Landing with the Marines were men from the 121st and the 18th Construction Battalions, together with small echelons of the 92nd and 67th Battalions.
Aslito airfield was captured on the fourth day of fighting, but not until the strip had been damaged by shells and was covered with shrapnel. It was decided that the northern side of the runway was easiest to repair, and the nest day, three companies of the 121st Battalion began work. Holes were filled with coral from stockpiles found near the edge of the field. Two Japanese road-rollers were found and put into operation.
By the end of the second day, the entire strip, 150 by 4,500 feet, had been repaired, and the first plane, a Navy TBF, landed. The Seabees were then assigned to unloading and storing aviation gasoline in Japanese-built gasoline-storage blockhouses. By D-plus-six, the runway had been widened to 200 feet. An Army aviation engineer battalion then took over the remaining construction, one company of Seabees remaining at the field to assist in laying marston mat. On D-plus-seven, Army planes began patrol operations from the field.
Seabees not assigned to airfield construction were occupied in unloading activities and repair of a Japanese pier.
On June 21, the 121st Battalion was ordered to repair the railroad from Charan Kanoa to Aslito Field, which had been badly damaged by shell fire. Four days later, the first train ran from Charan Kanoa to the field. Other railroads were soon repaired and running smoothly, and the Seabees then turned to road repair.
By July 1, American troops had captured the central part of the island around Mt. Tapotchau, gained control of the heights commanding Garapan and Tanapag Harbor on the west coast, and advanced to within 5 miles of the northern tip of the island. Organized Japanese resistance ended on July 9.
On September 13, 1944, the commander of the naval base presented to the island commander a plan for the development of a naval base, to include housing, boat-repair facilities, a seaplane base, tank farm, a naval supply depot, a naval hospital, an ammunition depot, fleet recreation areas, and general harbor developments. During October, the 39th, 17th, 101st, and 117th Battalions and the 31st Special Battalion arrived at Saipan to construct the naval base. In December, the 51st Battalion reported to augment the construction forces. CBMU's 595 and 614 were also assigned to Saipan in the fall of 1944.
On October 11, the 39th Battalion, assisted by CBMU 595, began work on the seaplane base at Tanapag. They found the site littered with wrecked Japanese planes, wrecked masonry buildings, the twisted steel framework of Japanese hangars, a damaged concrete seaplane ramp, and a demolished concrete apron. The badly damaged buildings were destroyed and the area cleared of wreckage. Work was pushed to make major repairs to the Japanese ramp and parking area, to secure adequate drainage, and to increase the operating area.
Housing was provided for 1,750 men in quonset
huts, and a 100-bed dispensary was erected. Quonset huts and steel arch-rib buildings were built for shops, and two portable seaplane hangars were provided. By the end of January, all work under the original plan for the base had been completed. During April and May, facilities were expanded to include an aviation supply annex, an aviation repair unit, and additional housing for 2,500 men. Expansion of the base also required drainage of a swamp.
Construction of a tank farm to supply fuel, diesel oil, and aviation gasoline for the Fleet as well as aviation gasoline for the seaplane base was started by the 39th Battalion on October 16, 1944. The tank farm was to consist of eighteen 1,000-barrel tanks for aviation gasoline, seven 10,000-barrel tanks for diesel fuel, and fifteen 10,000-barrel tanks for fuel oil, together with connecting pipelines, pump housing, and 1,200 feet of submarine line for each type of fuel. The work was greatly delayed by the lack of material. By the end of November, however, the tanks and lines for aviation gasoline had been completed. By V-J Day, seven of the fifteen 10,000-barrel oil tanks were in operation and the balance ready for tests; three of the original diesel tanks were in operation and the other four under construction. All lines from tanker moorings to the tank farms were completed in March.
In October 1944, the 17th Battalion began construction of a naval supply depot, which was to support the Fleet and shore-based personnel in the area. Two 100-by-300-foot transit sheds were rushed to completion to provide for 2,500 tons of supplies due early in November. The supply depot, completed in February 1945, consisted of 64 steel arch-rib warehouses, 11 refrigerator sheds, and 8 quonset huts for administration.
Another task of the Seabees was the erection of their own permanent camps and naval base housing for 3,200 men. The latter construction, the project of the 117th Battalion, included two 1,500-man galleys and mess halls. Ten double-deck barracks and an office were constructed adjacent to the housing development for use as a receiving barracks.
Before development of the naval base, waterfront facilities at Tanapag Harbor consisted of three beths for Liberty ships at an existing masonry pier and two at a 12-by-72-pontoon pier. The concrete ramp at the seaplane base was used for the discharge of LST's, LCT's, and LCM's. Harbor
development was the major task of the 117th Battalion, with the assistance of a detachment of the 301st Battalion, which had as its special mission the dredging of an entrance channel and the clearing of isolated coral heads to develop Tanapag inner harbor.
The naval base plan called for the establishment of a mobile repair facility sufficient to maintain and repair hulls and engines of craft assigned to small-boat repair units and a small-boat pool.
The mobile amphibious base repair unit consisted of five steel arch-rib buildings, one 3-by-7-pontoon barge, one 4-by-7-pontoon barge with a 12-ton crane, one 6-by-18-pontoon drydock with a 4-by-7-pontoon tender barge, three 2-by-24 pontoon piers, and two 30-ton ramps. Fuel storage for this unit was provided in four 10,000-barrel diesel-oil tanks and two 1,000-barrel aviation-gasoline tanks, erected by the 39th Battalion as part of the major tank farm.
The small-boat repair unit included one steel arch-rib building, two 2-by-12-pontoon barges, and one 4-by-6-pontoon wharf, and a 4-by-15-pontoon drydock, two quonset huts, and mobile machine shops.
A small-boat pool and LVT repair facilities were constructed on the site of an existing Japanese boat-basin. The Garapan pier, which had been partially repaired during the assault phase of operations, was further improved by putting in additional piling and coral-fill to provide 1,900 lineal feet of marginal pier, During the spring of 1945, the 101st Battalion erected two 7-ton cranes on 6-by-18-pontoon barges and constructed an ammunition pier at Garapan, together with a 900-by-22-foot earth and coral causeway.
An industrial area, established in the spring of 1945 consisted of eight quonset huts and nine steel arch-rib buildings, with access roads and utilities. Three steel arch-rib buildings and two quonset huts provided shops for the repair of base equipment.
An ammunition area, a project assigned to the 101st Battalion, involved the construction of 112 steel magazines, 20 by 50 feet, each; four torpedo magazines; shops and a motor-maintenance shed; coral-surfaced bunkers and parking areas; and more than 6 miles of access roads.
Naval medical facilities at Saipan were provided by small dispensaries at individual naval activities
and one 400-bed hospital constructed early in 1945 by the 17th Battalion. The hospital unit contained 40 quonset huts for wards, laboratories, mess halls, galleys, quarters, and administration buildings. Two steel arch-rib buildings with concrete decks and a refrigerator were constructed for general medical storage. The hospital was used for casualties from the Iwo Jima and Okinawa campaigns.
The major medical installations on Saipan were for the Army, and the Seabees assisted in the construction of several Army hospitals. In March 1945, the 101st Battalion was ordered to construct Convalescent Hospital No. 5, a 3,000-bed unit of tents with wooden decks. Work was started on march 25, and 1,000 beds with necessary facilities were ready eight days later. The hospital was completed on April 28.
On March 14, 1945, the 39th Battalion was assigned the completion of the 2,000-bed General Hospital 148, which had been under construction by the Army for seven months. The work remaining to be accomplished was the erection of 45 quonset huts, 20 prefabricated huts, all utilities, and improvements to galleys and mess halls. About half of the battalion worked on this project, with aid from 180 men of an Army engineer battalion, and completed the work by the end of April.
For Army General Hospital 39 and Army Station Hospital 176, each of 600-bed capacity, the 17th Battalion erected quonset and wood-frame buildings.
Construction of the huge Kobler and Isely air fields for B-29's on Saipan was essentially an Army engineering job, but Seabees assisted in the erection of housing and the installation of utilities. Two small fields were established by the Seabees, one at Marpi Point and one at Kagman Point.
The 51st Battalion began the construction of Marpi Field in January 1945 and had nearly completed the facilities by the end of April, when the balance of assigned construction was turned over to the Air Corps. The field had a 4,500-foot runway, 15,000 feet of taxiways and parking areas. 45 buildings, and several portable hangars. CBMU 616 assisted in the further construction of the field. The 101st Battalion operated the coral pit and hauled coral to the field. By the end of July, the field had been increased to include a second strip, 3,500 feet long, and a 1,400-foot addition to the original runway.
In April, the 51st Battalion was assigned to the partial construction and revision of Kagman Field. The existing coral-surface strip, 5,000 by 150 feet, was repaved, and additional facilities were built, including two portable hangars, a 1,000-man mess hall, and 58 quonset huts for quarters, shops, and utilities.
Another major project was the construction of an ammunition-storage area (500 acres) by the 101st Battalion. Many of the bunkers were located in hard coral, which had to be blasted, a process which slowed production and resulted in excessive break-down of equipment. The original plan called for 248 bunkers and 22 steel magazines. Plans were changed on January 15, 1945, to 109 bunkers and 197 steel magazines. Work progressed as rapidly as the arrival of equipment permitted.
On V-J Day, the 30th, 51st, 117th, and 121st Battalions, the 31st Special Battalion, and five maintenance units were at Saipan, the 121st Battalion having returned from Tinian in June.
The island of Guam, at the extreme southern end of the Marianas archipelago, the largest and most populated island of the group, is about 32 miles long and varies in width from 4 miles near the center portion to about 8 miles across both northern and southern sectors. The entire island is surrounded by an extensive reef system.
The northern portion of the island is a high limestone plateau with an average elevation of 400 feet, broken only by two higher points. Mt. Santa Rose and Mt. Barrigada. In general, the plateau is gently rolling and well adapted for the construction of airfields and related facilities. The southern part of the island has a rugged terrain and red volcanic clay soil which becomes very unstable under heavy rains.
The only important anchorage is Apra Harbor, on the western side of the island, formed by Cabras Island and Orote Peninsula. In spite of these protective arms, however, the harbor was open to
heavy ocean swells and required considerable development before it could be considered a first-class anchorage.
Island climate is healthful and pleasant. However, a 100-inch annual rainfall and a flash run-off which follows sudden downpours created considerable drainage problems.
Prior to the outbreak of hostilities in Europe, Guam had been under United States control since the close of the Spanish-American War and was the site of a small navy yard at Piti and a Marine barracks at Sumay. Early in 1941, a CPFF contract was negotiated for the construction of a naval station at Guam. Although the Hepburn Board in 1938 had recommended the development of Guam as a heavily fortified naval base and later, as a major air and submarine base, only minimum development was authorized under this contract because of the strained relations between the United States and Japan. Construction work was limited to tank farms for fuel oil, diesel oil, and motor gasoline; additional seaplane facilities; together with housing, power, water, and roads.
Contract construction started on May 24, 1941, with the erection of five steel tanks for oil storage, and the next project was road construction.
Construction on the breakwater on Luminao Reef, to afford greater protection against typhoons than was given by Cabras Island, was not started until August 1941. Huge limestone blocks, quarried on Cabras Island, were skidded along the reef to an improvised derrick which deposited them at desired points to form the breakwater.
A crew of experienced steel workers from the mainland was employed in the erection of the steel tanks. Other projects were carried out for the most part by native labor. Two other construction organizations worked in conjunction with the contractor's organization. One was the Guam naval station public works force, consisting of about 1,500 military and native personnel, who worked on the breakwater and oil pier, and on the development and extension of power, water, communications, and sewage-disposal system. The other organization, operated under the Island Department of Industries, had a personnel of about 800 natives, chiefly concerned with road building and maintenance. Practically all construction equipment, plants, and utilities used by the contractors were facilities of the naval station, the Marine Corps post, or the Island Government maintenance department.
Work on the construction projects was scarcely well underway when Guam was taken by the Japanese on December 10, 1941. A road had been extended and improved. One mile of breakwater, 36 feet wide and 5 feet above sea-level, had been completed. An oiling dock had been constructed
and piped, and some work had been accomplished on pump houses, barracks, and mess halls.
The contractor's organization had also done engineering and experimental work in connection with a proposed Orote Peninsula airfield. In a letter of August 6, 1941, the naval commandant reported surveys indicating that a 4,500-by-400-foot landplane runway could be constructed.
No action was taken by the United States on this proposal, but the Japanese, during their occupation, recognized the suitability of the location and constructed, a 4,500-foot coral-surfaced airstrip on the peninsula. In addition, the Japanese brought a similar strip northeast of Agana to near-completion and partially cleared a third strip still farther north. Otherwise, the Japanese did very little to improve or extend the island facilities.
The United States assault to recapture Guam began on July 21, 1944, when landing forces struck at two points, one about 2 miles north and the other about 2 miles south of Apra Harbor. In the north, the assault was spearheaded by the Third Marine Division (Reinforced), which stormed and broke the defense on a beachhead extending along the west shore of the island, from Piti to Asan. In the south, the First Provisional Marine Brigade and the 77th [Infantry] Division struck on the beaches of Agat, forcing a beachhead along the west shore, from Orote Peninsula southward to a point beyond the village of Agat. By the evening of D-Day, assault forces had secured firm footholds ashore, and were driving inland against considerable infantry, automatic-weapon, and mortar-fire opposition, to force a north-south junction and so cut off Apra Harbor and the surrounding hill country.
The 25th Construction Battalion, one of several Seabee units active in the assault, landed with the Third Marine Division on the northern beaches near Asan. Acting as a shore party for the Third Combat Team, this unit had charge of Red Beaches One and Two, where landings were effected rapidly in the face of enemy fire. Personnel of this shore party were subjected to considerable fire throughout the first three days of assault operations. The 25th manned beach defenses in this area until increased security of the beachhead made it possible
to reduce these forces, and also provide rear guards in the combat lines.
On the fifth day of the assault, four 25th Battalion road repair units were brought ashore, and the road leading from Piti to the principal city of Agana wax repaired for the advance. The remainder of the personnel of this unit was assigned as ship's platoons and acted as stevedores in unloading essential cargo for the assault troops.
Company B of the 2nd Special Battalion also took part in the Asan landings. This unit, consisting of six officers and 201 men, was assigned to working the supply dumps by day and occupying ridge defenses by night.
After July 28, the men and equipment of the 2nd Special were transferred to the southern beachhead, where the major part of unloading operations was in progress. On September 9, the remainder of the battalion arrived. The entire battalion then moved to a new camp location and swung into its regular routine of handling cargo from ships unloading in Apra Harbor.
CBMU 515 was attached to the 22nd Regiment of the First Provisional Marine Brigade and hit the southern landing beaches near Agat with the first assault waves. Casualties were numerous. Two sections of this unit were engaged in actual fighting for the first two or three hours after landing. The mission was to handle all equipment for the battalions and staffs of the 22nd Marines and to unload supplies for the inland assault. Cargo-handling across the reef was accomplished under continuous sniper fire. Late in the afternoon of D-Day, a bulldozer and a welding machine were landed and work was immediately started on the repairing of damaged LVT's.
CBMU 515 was assigned to night rear-guard duty for nearly a week. As equipment came ashore, road-building and supply of front-line Marine troops were carried on. As the fighting progressed northward, two Marine hospitals were erected.
A special group of the 53rd Battalion, composed of one officer and 18 men, landed just four minutes after H-Hour. Theirs was the difficult mission of
anchoring landing craft, LCT's and LCM's, at the reef edge, using waterproofed tractors, while the craft discharged their cargoes of armored field tanks. After securing the landing boats, the men marked out a lane, through waist-deep water, across several hundred yards of reef to the beach, and led the incoming tanks safely ashore. This work was carried on for more than nine hours under constant enemy fire, during which time some 50 LCM's and five LCT's were unloaded.
On July 22, the entire forward echelon of the 53rd Battalion, 18 officers and 520 men, went ashore to further assist in landing operations. In addition, the men hauled supplies, built combat roads, repaired bridges, established water points, and set up command posts. The second echelon came ashore on July 27. During the early phases of the assault, the battalion cleared the areas of some 23 tons of explosives.
Another Seabee outfit which had a hand in the assault phase was the 13th Special Battalion. Men from this unit landed with the southern forces on July 28. One man was wounded when enemy troops on Orote Peninsula opened up with mortars on the unloading LST's. On July 30, Orote Peninsula was secured, and the next morning the first vessels entered Apra Harbor. Before noon of that same day, the 13th Special had five stevedore crews aboard these ships. Unloading, without benefit of piers or established points, began at once,
with small landing craft and self-propelled barges serving as lighters.
Meanwhile, the Japanese airstrip on Orote Peninsula had been cleared of enemy resistance on July 28 and was placed in operation the next day by the 2nd Marine Engineer Battalion.
On July 23, both the Island Commander, United States Marine Corps, and the Officer-in-Charge of the Fifth Construction Brigade came ashore with the assault forces at Agat. Operational control of all construction forces during the initial assault phase was administered by the Marine general commanding the assault forces. As enemy forces were eliminated from portions of the island, permitting occupation and base development by our forces, construction forces, such as the 2nd Marine Engineer Battalion and the 25th and 53rd Construction Battalions, were placed under the control of the Fifth Brigade Commander.
Organized resistance on Guam was officially ended on August 10, 1944, but enemy resistance from caves, jungles, and hillsides continued for many weeks. The Seabees had a least a small part of the subsequent mopping-up. Additional Seabee units came ashore shortly after the initial resistance had been overcome, and on August 15, 1944, the 5th Brigade assumed control of the island construction work.
The large-scale assault operations carried out by our attacking forces, together with minor demolitions set off by the Japanese, had destroyed a major part of the installations on Guam. Agana, the principal city and capital of the island, with a pre-war population in excess of 12,000, was utterly destroyed in the bombing and shelling of the assault. Two other towns of importance, Piti and Sumay, located on Apra Harbor, were also leveled by pre-invasion bombardments. With the exception of the Piti boat channel and quay-wall, and the breakwater and oil dock at Cabras, all naval installations on Guam were damaged in the assault beyond any possible use except as a source of salvaged materials. Of the extensive water system, a large part of the overland pipeline was destroyed during the assault, but the reservoirs remained practically intact. The pre-war road system was also badly damaged by the bombardment and the greatly increased traffic. The only construction
work by the Japanese which could be used by our forces were the three airstrips.
Development of waterfront facilities in Apra Harbor was a task of highest priority. The tremendous importance of the harbor to base development had been recognized in the choice of an assault site. As the natural barrier reef precluded any considerable use of LCT's and the existing pier installations were negligible, the Seabees began the installation of pontoon piers to break a prospective bottle-neck of supply.
It was decided that the logical spot for installing the first pier was the site of an old Navy fuel station on Cabras Island. Blasting was first necessary to obtain a 35-foot depth of water along the outboard face of the pier. Construction was initiated on August 5, 1944, and the pier was completed by August 22.
All the actual pontoon-assembly work was done in deep water by a crew of Seabees quartered aboard an LST in the harbor. At the same time, another crew built a coral-fill causeway out to the pontoon string. Soon, pontoon piers were being completed on the average of one every twelve days, in spite of bad weather, rough water, and the scarcity of material.
By the first of October 1944, six piers, 42 by 350 feet, were in full operation, and a seventh was under way. In the meantime, five concrete barges had been sunk for a temporary breakwater extension along Balalan Bank. Then disaster struck. A full-scale typhoon passed near Guam between October 3 and 9. Continued strong winds built up such heavy waves in Apra Harbor that they destroyed or severely damaged all the pontoon piers, carried away portions of the Cabras Island breakwater, and seriously damaged the sunken barges placed to form the breakwater extension. When the weather finally cleared and the heavy seas subsided, the supply problem was more critical than ever.
One pier at Sumay and one at Cabras were repaired as quickly as possible to permit time to redesign the construction of the others. One month after the typhoon, seven piers were again in full operation and in a more secure condition. A new elastic bridge connection was designed to absorb the shock of the tide rather than attempt to resist it. The "Hensen" connection is made from a steel
I-beam, welded to the pontoon bridge and clamped to the anchor string by a coil spring and a pendulum-type rod which allows the I-beam to slide back and forth on the anchor.
Two other phases of waterfront construction involved the breakwater along Calalan Bank and the development of the inner harbor. Limestone, quarried on Cabras Island, was used to construct the breakwater, 3,260 feet long and 32 feet wide. The entire protective arm, which was built along the north of Apra Harbor, from the main island through Cabras Island to the outer tip of the breakwater on Calalan Bank, measured 17,000 lineal feet.
Development of the inner harbor included 7,500,000 cubic feet of dredging and the construction of 26,000 lineal feet of quay wall. The quay walls were built with steel sheet-piling, back-filled with coral. A small-boat pool and a submarine base with a finger pier were provided in this part of the harbor. Existing installations at Piti for small-boat repair were rehabilitated and augmented.
By July 1945, the piers in Apra Harbor numbered 14 quay-wall berths, nine pontoon piers, two wooden piers for fueling, ten LST berths, and one submarine pier.
As the waterfront facilities were developed to accommodate the heavy flow of supplies and equipment, other construction on Guam proceeded apace. Of prime importance was the establishment of five airfields to support the offensive operation of heavy, long-range bombers against the islands of Japan. The three Japanese strips, which had been captured in varying stages of completion, formed the nucleus of the first three fields to be established. In addition, two huge fields of two strips each were constructed on the northern tip of the island for B-29 bases.
Orote Field, which had been completed by the Japanese to 4,500 feet, and was the only existing strip to be rehabilitated during the assault, was completely rebuilt and lengthened to 5,500 feet by the Marine Engineers. Seabees assisted in the development of the field, constructing hardstands, shops, and warehouses. Orote Field was in constant use after the early part of August 1944, first for fighter operations and later for conditioning 1,800 planes per month for the Fleet and the Marines. Planes were tested, repaired, and cleaned of the preserving compounds with which they had been shipped overseas. An aviation supply depot and an aircraft repair and overhaul unit were established at the field.
The second step in airfield construction was on the 5,000-foot strip which the Japanese had almost completed near Agana. The initial runway was extended to 7,000 feet and paved with asphalt, and a second asphalt-surfaced strip, 150 by 6,000 feet, was constructed. The field was rotated several degrees in order to reduce flight interference from
Mt. Barrigada. The first planes landed on the former Japanese strip on August 29, 1944, and the field was commissioned on October 22. Agana Field was used principally by Naval Air Transport Service and for Army passenger and freight traffic.
The Japanese had completed clearing a third strip, to the north of Agana Field. This site was chosen for the establishment of Depot (later, Harmon) Field, and again the orientation was shifted slightly. Two inches of asphaltic concrete were applied to the 7,000-by-150-foot strip; 12,000 feet of taxiway and 42 hardstands were constructed.
Eight superstructure hangars, 130 by 160 feet each, and ten 160-by-190-foot repair hangars were erected for the field. Cooperation between the Army Engineers and the Seabees produced the largest air repair base in the Pacific for the repair of B-29's in the Marianas. The first B-29's landed on November 24, 1944.
Early in 1945, attention was concentrated on the carving of the two B-29 fields, North and Northwest Fields, out of the dense jungle on the northern end of Guam. Each field comprised two asphalt-surfaced runways, 8,500 by 200 feet, capable of sending off 160 planes per flight.
North Field was constructed entirely by Army Engineers. The first strip was commissioned on February 3, 1945, and three weeks later, the first B-29 Tokyo raid from Guam was launched from this strip. By the end of April, the second strip was in operation.
During April and May 1945, the combined efforts of the Army Engineers and the Seabees were centered on the construction of Northwest Field. In the construction, 26-foot cuts and fills were made through hard limestone. The south runway, completed two days ahead of schedule, was opened to service on June 1, 1945. Work was rushed on the taxiways, hardstands, and operational facilities for the south strip and also on the second strip and its appurtenances to accommodate the rapidly arriving B-29's. The north strip was in operation by July 1.
Another vital construction project on Guam involved the development of a road network. Road construction was undertaken during the rainy season, while the invasion battle was at full tempo. It was a road job different from, and more difficult than, any previously attempted in the Pacific. The terrain presented considerable difficulties, because
the rugged outcroppings of rock and sharp shoreline required heavy earth moves. Moreover, the roads were to be permanent.
Specifications were as rigid as those for superhighways in the United States. Main arteries were to be widened to 56 feet and made to carry four 11-foot traffic lanes. Curves on the main roads were not to exceed six degrees, and grades were to be held to a six-percent maximum. Primary roads were surfaced with two and a half inches of asphalt; secondary roads were surfaced with coral and then oiled. Secondary roads would carry either three or two lanes, but this reduction in width did not relax any of the other rigid criteria.
The first major road job undertaken was the construction of a super-highway between Sumay and Agana. Three weeks after D-Day, the road was under construction. Constant two-way traffic made construction progress almost impossible; torrential rains reduced every new cut to an ever-deepening gumbo and made the problem of fill acute; breakdowns in equipment came rapidly; and road workers had to take precautions against Japanese snipers. A high expenditure of coral was necessary where the road was built across gullies, swamps, and former rice paddies; these sections took between 10and 18 feet of fill. At the end of 60 days, a four-lane highway, 12 miles long, had been constructed, with nine bridges built to standard H-15 highway loading. Traffic on this main highway reached a proportion equal to the traffic in downtown sections of large cities in the United States.
Attention was then turned to regrading and straightening other existing roads and to building new roads for access to airfields, ammunition dumps, camps, and other facilities. The road network on Guam finally totalled more than 103 miles.
Due to the position of Guam in the forward area, it was essential that a large store of supplies, spare parts, equipment, fuels, and refrigerated foods be on hand at all times for the Fleet and for military forces on the island and in forward movements.
By March 1945, an extensive tank-farm system was completed. Storage had been provided for 328,000
barrels of aviation gasoline, 130,000 barrels of diesel oil, 40,000 barrels of motor gasoline, and 448,000 barrels of fuel oil.
Several major supply depots were established. The naval supply depot comprised 464 steel arch-rib warehouses, a large personnel camp, open storage areas, a drum filling plant, and 68,000 cubic feet of refrigerator storage.
The advance base construction depot covered 250 acres and had 360 buildings for general warehouses, spare parts storage, equipment overhaul and tire repair, and a 2,600-man camp. The function of the depot was to procure, store, and issue supplies and equipment, primarily for the Seabees, but equipment was issued to other military activities when available and if priorities warranted the issue.
The Marines had cognizance of the issue of all the staple foods on the island, which necessitated large warehouses. Five 96-by-540-foot buildings
were erected at Agana, and two at Agat, one 745 by 118 feet and the other 349 by 118 feet, for this purpose.
The medical supply depot was composed of 18 buildings. Total warehouses for all airfields consisted of more than a million square feet of space. The Marine depot for supplies was made up of 190 buildings. Army garrison forces had about 600,000 square feet of storage space.
The naval ammunition depot consisted of two sections, one for the Fleet and one for ground forces. The Fleet unit comprised 44 quonsets for personnel and administration buildings, 202 prefabricated steel magazines, 100 hardstands, and 20 fuse magazines. The ground unit had 26 quonsets, 550 shelters, 61 hardstands, and 50 magazines.
The water system on Guam at the time of the invasion was insufficient, because of bombardment damage and initial inadequacy, to meet the needs of the tremendous increase in population and the demands of the Fleet. Various methods were used in the development of an adequate water system. Shallow wells along the coastal areas, deep wells in the interior, a basal ground-water tunnel, dams, and springs were used until the total completed water system had a capacity of 12,000,000 gallons per day from 67 main sources.
The Almagosa system was the largest, supplying two million gallons per day for Orote Peninsula and for the Fleet. It consisted of a 12-inch pipeline from Talofofo River, paralleling the main 10-inch line from Almagosa Springs to tanks at Orote, for facilities and docks at Orote; a 6-inch pipeline loop for Orote facilities; and 10-inch pipelines from tanks to docks.
The Agana system supplied one and a half million gallons per day to the towns of Agana and Sinajana and units in the vicinity. The Ylig treatment plant, producing 300,000 gallons per day, consisted of plant pumps and pipelines to various activities in that area. The Pago River treatment plant, with rapid sand filters, provided 500,000 gallons per day to mobile combat units in that vicinity. A 400-foot underground tunnel, with pumping stations, supplied
Barricada Radio Station (above) and Marine Corps Field Depot (below), Guam
one million gallons of water per day for Agana Field, the ABCD, and the Fleet hospitals. Deep and shallow wells and the dams produced water for all the other activities.
Hospital construction on Guam was initiated in September 1944. By March 1945, the hospitals, brought to usable completion by Seabees and Army Engineers, provided a total of about 9,000 beds and were pressed into service to handle casualties from the Iwo Jima operation. Included were Naval Base Hospital 18 (1,000 beds); Fleet Hospital 103 and 115 (1,000 and 2,000 beds, respectively); the 373rd Army Station Hospital (750 beds); and the 204th Army General Hospital (1,000 beds).
Devastation of civilian housing on Guam, as a result of bombing and naval bombardment, was extensive. There were few habitable buildings in the town of Agana, Asan, Agat, and Sumay. Approximately 15,000 natives had to be housed, and three camps were set up at Agana, Agat, and near the Ylig River. Each camp had its own hospital with a total capacity of about 150 beds. Screened food-preparation centers were provided, and food was distributed from the preparation center. Water and sanitary systems were set up. The camps were crowded and accommodations in many instances were primitive, but the civilians were returned to their own ranches, farms, and houses as soon as practicable.
Development of the major advance base at Guam was accomplished by the cooperative efforts of the Seabees, the Army Engineers, and the Second Marine Engineer Battalion. Free interchange of equipment and materials was made possible by the operational control of the Fifth Brigade over all construction forces. The Seabees were responsible for approximately 75 per cent of the total construction.
Very little native labor was employed in construction, primarily because most of the natives were needed on the reconstruction of their own homes and on Federal Economic Administration
farming projects aimed at producing fresh foods for natives and for garrison forces.
In all, some 37,000 construction troops were employed in the construction of Advance Base Guam.
The northern part of Tinian contains an extensive plateau ideally suited for a large airdrome, a circumstance that had not been overlooked by the Japanese. During the months just prior to our Marianas offensive, they had done considerable work there on two airstrips, one a coffin-shaped field, 4,700 feet long, and another of more orthodox shape, 3,900 feet long. In addition, they had completed a 5,000-foot strip about midway of the west coast, and had begun a small runway near the center of the island. Japanese construction on the northern plateau formed the nucleus of the great airfields the Seabees built on Tinian during the succeeding months.
In view of the magnitude of the development planned for Tinian, the Sixth Construction Brigade was formed and was assigned responsibility for all construction work on the island. It comprised, originally, the 29th and 30th Construction Regiments; later, while base development was in progress, the 49th Regiment was formed and became part of the Brigade. Two of the battalions, the 18th and the 121st, participated in the assault on Saipan and were again given an assault assignment in the Tinian invasion. As was customary, during the assault period these battalions were under Marine Corps control and did not formally become part of the construction brigade until the island was secured.
The invasion of Tinian was principally a shore-to-shore operation from Saipan by landing craft. On July 24, 1944, the Fourth Marine Division landed on two narrow beaches on the northwest coast of the island. They were accompanied by the
forward echelons of the 18th and 121st Construction Battalions. The remaining personnel of these battalions went ashore on Tinian on July 27.
The 18th and 121st had a different organization than was customary for construction forces assigned to Marine divisions. The men had been especially trained, prior to the occupation, to perform certain tasks that could be activated according to operational requirements in the field. Twelve assault units were set up, as follows: LCT ramp maintenance, beach access, road reconnaissance, road construction, road maintenance, traffic circulation, railroad demolition, railroad construction, airfield rehabilitation, civil affairs construction, water supply, and reserve.
One of the more significant tasks of the Seabees in the Tinian assault was the maintenance of LVT ramps -- especially developed services to allow LVT's to climb the steep banks that flanked the narrow landing beaches.
The ramp consisted of two side-rails, made of 10-inch I beams, which supported an articulated mat of 6-by-12-inch timbers, and was carried to the landing point by the vehicle itself. The side rails were suspended from the sides of the LVT, with enough upward slope to permit their forward ends to clear the top of the bank. The timber mat was supported for its first 10 feet by the rails and for the remainder of its length by slides built over the vehicle's cargo well. At the point of landing, the forward ends of the rails were released so that they came to rest on the top of the bank; the LVT then backed away a few feet, allowing the after ends of the rails to rest on the bottom. Further backing permitted the timber mat to come to rest upon the rails for its entire length, and the vehicle could then go ashore over the ramp thus formed.
The first echelon of the 18th battalion installed and maintained these ramps, the work lasting three days. Harbor facilities were non-existent and everything had to come across the barrier reef, to be unloaded and transported inland.
Upon arrival of the remainder of the battalion, road-repair and construction details were assigned, emphasizing the construction of special roads for cleated vehicles. The terrain was level, and access roads were easily built from the beaches to the existing Japanese roads.
On July 27, the 121st Battalion began the repair of the 4,700-foot Japanese strip in the north, filling bomb and shell craters with swept-up shrapnel fragments. By evening, a strip, 150 by 2,500 feet, had been repaired. The next day, the first plane landed. At the end of two days the field had been repaired for its full length, and on the third day, the Seabees widened it to 200 feet. Air transports immediately began operating from the field, bringing in supplies and evacuating wounded.
A few days after the initial assault, the surviving defenders fled to a network of caves in the hills and cliffs of the island; on August 1, the assault phase on Tinian was over. The Seabees were thereupon
released from the operational control of the Marine commander and were assigned to the Sixth Construction Brigade, which began its full functioning on August 3.
Plans for the development of Tinian as a major air base had been carefully laid at Pearl Harbor during the months preceding the invasion, by a nucleus staff of the Sixth Brigade in cooperation with the 64th Army Engineers of the Army and the joint staff agencies of the area command. According to the plan adopted, two strips built by the Japanese, the 4,700-foot strip at the north end of the island and the 5,000-foot runway on the west coast, were to be extended to 6,000 feet each so that medium and heavy bombers could operate from them. After that extension had been made, the northern runway was to be lengthened to 8,500 feet and the neighboring Japanese-started strip was to be completed to the same length, to support the opening operations of B-29's. The next scheduled step was to be the building of two more 8,500-foot strips on a new site in the vicinity of the west coast strip. In addition, a field, having a 6,000-foot runway, for Navy use, to be designated East Field, was to be built at a location to be determined on the scene.
Immediately following the securing of the island the air base development was begun, but the plan was modified. The rehabilitated northern strip was extended by 1,000 feet at its west end and 650 feet at the east end and was widened to 300 feet. This strip formed the first element of what later was to
become the great North Field. The second task, undertaken in September, was the completion to a 6,000-foot length of the neighboring Japanese-started strip; thereupon, designated North Field, Strip No. 3. The existing Japanese field on the west coast of the island, which had been severely damaged during the assault period, was then reconditioned to serve as a 4,000-foot fighter strip.
During this early period, Navy patrol planes operated from the North Field runways. When the time arrived for enlarging those strips to permit their use by Superfortresses, it was necessary first to provide a new field for the Navy's use. A site, a mile east of the west coast fighter strip, was chosen, adjoining the area selected for the proposed third and fourth B-29 strips; construction of a new 6,000-foot runway, designated West Field, Strip No. 3, was put under way. The East Field site, originally planned for the Navy field, was rejected as unsuitable for proper development. To expedite the construction of the Navy strip, on October 1 practically all construction at North Field was brought to a halt and all the heavy-duty earth-moving equipment on Tinian was moved to West Field. By November 15, the strip was complete, and the entire Navy air force moved to its new base. Accessories to this strip included 16,000 feet of taxiway, 70 hardstands, 345 quonset huts, 33 buildings for repair and maintenance facilities, 7 magazines, and a 75-foot-high control tower.
After the completion of the Navy air facilities at West Field, attention was directed again to North Field and to the extension and strengthening of the two 6,000-foot bomber strips to fit them for Superfortress use. At the same time, the scope of the plan for North Field was enlarged, calling for four B-29 strips instead of two.
The North Field project was assigned to the 30th Regiment, when, in turn, divided it into several phases and assigned principal responsibility for each phase to a battalion.
The first phase was the development of Strip No. 1, to its required length of 8,500 feet and width of 30 feet, and the construction of taxiways, hardstands, and aprons necessary to serve it. The 1211st Battalion, which had rehabilitated the old Japanese strip in this location during the assault period, was named as "lead battalion" for this phase. The other battalions of the 30th Regiment assisted it, acting as sub-contractors. Strip No. 1 was completed nine days ahead of the date set. The first B-29 landed on December 22.
The second phase included the extension of the No. 3 strip to 8,500 feet, with the 67th as the lead battalion.
The 13th Battalion drew the responsibility for the next phase, which was the construction of a strip, designated as North Field No. 2, between the two earlier strips, including taxiways, hardstands, and a service apron for a projected fourth strip. Strip No. 2 was completed and received its first long-range bomber on February 27.
Instead of proceeding immediately with construction of Strip No. 4, all construction effort
was then directed to the development of the long-range bomber strips planned for West Field.
Construction of West Field, Strip No. 1, the first B-29 strip at that location, north of the Navy's West Field strip (No. 3), had been begun on February 1 by the 49th Regiment, a newly formed unit; in March, the battalions of the 30th Regiment were added to the project.
Construction of two 8,500-foot strips proceeded simultaneously, and personnel and equipment from all battalions were freely exchanged in accordance with the needs of the job. Both strips, laid out parallel to each other, were 500 feet wide and included 53,000 feet of taxiway, 220 hardstands, 2 service aprons, sub-service aprons, and warm-up aprons, 251 buildings for administration, repair, and maintenance, and 4 personnel camps. On April 2, Strip No. 1 received its first B-29's. Strip No. 2 was completed on April 20.
After West Field was finished, the 30th Regiment again took up its unfinished work at North Field. Under the leadership of the 135th Battalion, the fourth 8,500-foot strip was constructed to a width of 500 feet. In addition, the other three strips were widened to 500 feet and additional hardstands were built. On May 5, 1945, North Field, Strip No. 4 was complete.
Total facilities at North Field, in addition to the four 8,500-foot runways, comprised 8 taxiways, aggregating nearly 11 miles, 265 hardstands, 2 service aprons, 173 quonset huts, and 92 steel arch-rib buildings. The four runways were parallel 1,600 feet apart, with taxiways in the intervening spaces. Construction of the field would have been simpler if the runways had been only 7,000 feet long, the width of the Tinian plateau. The last 1,500 feet spilled over the edge of the plateau, and extensive fills had to be made on both the east and the west sides of the island. Moreover, after construction work had started the maximum permissible taxiway grade was reduced from two and one-half to one and one-half per cent, because of an operational decision to taxi the planes under their own power to take-off line, instead of towing them by tractor as originally planned. This change increased the amount of earth to be moved at North Field by 500,000 cubic yards.
The construction of the Tinian fields represented a gigantic earth-moving operation. Deep cuts in hard coral and high fills characterized the work at both North Field and West Field. Cuts as deep as 15 feet and fills as high as 42 feet had to be made. North Field excavations totalled 2,109,800 cubic yards, and the amount of fill required was 4,789,400 cubic yards. At West Field the quantities of cut and fill were 1,718,050 cubic yards and 3,298,490 cubic yards, respectively. The great volume of excess fill necessitated development of huge borrow pits in the coral underlying the island.
Before the airfield program was put under way, test holes were dug to determine the extent of the over-burden and the characteristics of the underlying coral. They showed that the over-burden was usually from 8 to 12 inches deep, but that in certain areas there were soil pockets of considerable depth which characteristically occurred between hard
coral heads that would be difficult to remove. Shortly after the beginning of these investigations, a soils expert was sent out from the office of the Director of the Pacific Division, Bureau of Yards and Docks, to study the many problems encountered and to assist in finding solutions that would assure runways able to support the heavy loads imposed by Superfortresses. This work was later carried on by a soils engineer on the brigade staff.
The design adopted for the fields required that the rolled-coral base course be not less than 6 inches thick where the sub-base was of pure coral, free of soil pockets. Where the pockets were deep, or where there were fills of relatively stable overburden, a base-course thickness of not less than 21 inches was specified. After construction was under way the 21-inch requirement was relaxed to 18 inches, after tests of the shear value of compacted coral had demonstrated that the thinner base course would suffice to distribute the weight of prospective wheel loads.
Soil tests were continued throughout the entire construction period by six field parties. All test data were studied at a soils laboratory, set up at a battalion engineering office. Among the facts learned about Tinian coral, was the discovery that it had a 45-percent compaction factor.
The method of construction had to be studied individually for each runway. For example, the determining factor for procedure on West Field No. 3 was the availability of only twelve wagon drills, an insufficient number to permit making enough cuts to balance the volume of fill. Under the circumstances, rooting and panning were practiced as long as practicable, but upon encountering large coral heads of crystalline limestone, it was necessary to abandon this procedure in favor of mass hauling from borrow pits. About 400,000 cubic yards were hauled a distance of 3 miles; during the 45-day construction period a total of more than 1,000,000 yards had to be moved.
Similarly, on North Field, the shortages of wagon drills did not permit cutting through a heavy bank of coral at the east end of the field, and made it necessary to use two heavy tractors with each pan. This was hard on equipment, but the permitted construction period was short.
In the early phase of the extensive dynamiting operation, material was blasted to a depth of a foot below sub-grade. It was soon discovered, however, that considerable follow-up was necessary to remove the coral heads that were left protruding above grade. The depth of the drilling below grade was subsequently increased from 2 to 3 feet to reduce the clean-up grading.
Coral on Tinian was considerably harder and more irregular in structure than that on Saipan and Guam, and, in view of the tremendous quantities
that had to be handled, it was highly desirable to find borrow pits that could be dug with a shovel without extensive dynamiting. The coral pits developed on Tinian fell into three categories:
(a) "Push Pits," in which coral could be pushed by a bulldozer working down a slope to a point where it could be shoveled into trucks.
(b) "Bailing Pits," in which the coral could be dug by power shovels, without preliminary blasting.
(c) "Blasting Pits," in which blasting was necessary.
Though it was desirable that borrow pits be located as near the airfields as possible, to minimize hauling time, it was found that a good "bailing pit" was advantageous even when the haul was relatively great.
It was also found that on deep fills, the pocketing of water during heavy rains caused unstable sections if the relatively flat transverse grades were maintained. To avoid this, all fills were started on the center line, and the lifts were brought up with not less than 5 percent cross-grade, to permit rapid runoff, until the top level was reached. Then, working with coral alone, the transverse grade was gradually brought up to meet the flat grade specified. The rapid placement of fills almost 50 feet deep may be credited to the adoption of this procedure.
Earlier Seabees experience in other specific locations had shown salt water to be the best stabilizing agent for coral. The speed with which the fills had to be made on Tinian and the limited number of trucks available, however, made it impracticable to haul salt water in sufficient quantities. Moreover, compaction tests of the completed surface, especially where the fill had been placed in small lifts which had been extensively rolled with a sheepsfoot roller, indicated that the densities were practically as great with fill placed in the dry as with fill placed in the wet. In later phases of construction, the use of salt water was eliminated except for the final finishing.
In the finishing of the surface, a honing process, using patrol graders, brought the fines to the surface.
At this stage, it was essential that adequate salt water be applied, to improve the cementing action of the coral particles, and to eliminate dust during the early field operations. These surface ultimately were to be topped with asphalt, but during the immediate operational stages it was imperative that frequent salt-watering be practiced as a dust palliative.
As a final step in the airfield development program, runways and taxiways were paved with asphaltic concrete, 200 feet wide. The asphalt was placed to a thickness of two and one-half inches and rolled to slightly more than two inches.
During the early part of base development, all fuel consumed on the island was obtained from drums. Later, facilities were installed in Tinian Harbor for obtaining bulk aviation gasoline from a steel barge, known as YOGL. Although this method necessitated trucking gasoline for 10 miles, over narrow, congested roads, the YOGL was an improvement over the dangerous and arduous system of drum-dumping.
Tank-farm construction was started in early September 1944. On November 3, after the construction of 25,000-barrel storage capacity, all future tank-farm construction was turned over to the 29th Regiment, which, in turn, assigned the 18th Battalion as "lead" battalion on the project. By November 27, 1944, a submarine pipeline and 56,000-barrel storage space were ready for use by the first tanker. The entire project was completed by March 8, 1945.
The island fuel system, as completed, consisted of a single 14,000-barrel storage farm for diesel oil, one 20,000-barrel farm for motor gasoline, and a series of six farms, with capacity of 165,000 barrels, for storage of aviation gasoline. All fuel was brought ashore through a submarine pipeline, from a single tanker mooring just north of Tinian Harbor. Numerous pumping stations and 86,000 feet of main pipeline distributed fuel over the island. The diesel-oil and motor-gasoline farms were located close enough to the tanker mooring to be filled from the tanker's pumps. Each was fed by a 6-inch line which permitted a filling rate of 700 to 800 barrels per hour. The aviation-gasoline storage was divided into two main farms and four secondary farms located near the two airfields. The system had six dispensing points for North Field and two for West Field.
Seabee ingenuity was called upon when the unforeseen expansion of airfield facilities necessitated the moving of an already completed aviation-gasoline tank farm of twelve 1,000-barrel, bolted-steel tanks to a new location about a mile distant. A method was worked out by the 18th Battalion to move the tanks intact, thus saving considerable time and material. The job was completed in five days.
In the selection of Tinian as a B-29 bomber base, because of its potentialities for development as a large airfield, consideration had to be given to the absence of any natural harbor. The only site on the island that was conceivable for a harbor was at Tinian Town, where the southwest side of the island formed a slight bay in which it was possible to anchor five or six ships at one time.
Waterfront construction was divided into two phases. The first phase lasted from D-Day until the middle of November, when all effort was directed to building and maintaining temporary facilities. When the island was secured, our forces found themselves in possession of two small beaches capable of accommodating landing craft, a pontoon pier constructed by the assault forces, and two badly damaged Japanese masonry piers.
In August, two temporary marine railways for use in repairs to LCM's and LCVP's were built. A section base was started about a mile south of Tinian Town, but was abandoned because the location was too unprotected. A severe storm in early October destroyed the two railways, the existing work at the section base, the pontoon pier, and one of the masonry piers. To alleviate the critical situation resulting from this damage, a pontoon pier was constructed of three sections of 4-by-30 strings, connected by flexible bridges which enabled the pier to withstand the shock of rough water.
The second phase covered the period subsequent to the middle of November and involved the construction of permanent harbor facilities. The major project for this period was the provision for berthing eight Liberty ships.
The 50th Battalion, which arrived in November 1944, was designated to accomplish the permanent waterfront work at Tinian. Before the arrival of the 50th, the 92nd Battalion had driven about 120 lineal feet of sheet-piling along what was to become the south bulkhead. The 107th Battalion had done some grading along the waterfront and had built a ramp extending from the shoreline to a
point on the coral reef, about 1,150 feet distant. This ramp later formed a portion of the breakwater.
The project for the berthing of eight Liberty ships consisted of three component parts. The south bulkhead, that portion of quay wall paralleling the pontoon pier, was 600 feet long. The cargo ship bulkhead formed that part of the quay wall which turned from the south bulkhead, at an inside angle of 75 degrees, and extended northward for 2,000 feet. The cargo ship piers consisted of two sheet-pile piers, 80 by 500 feet each, running parallel to the cargo ship bulkhead and connected to it by a causeway, 88 feet wide. The project was started in late November 1944 and was completed on March 6, 1945.
The breakwater at Tinian Harbor, built on an existing coral reef that fringed the small harbor, was of circular cell design. The 120 circular cells, built of sheet piling, were 30 feet in diameter, plus-15 grade above mean low water, and were filled with coral.
Considerable dredging was necessary for the development of the harbor. A detachment of the 301st Construction Battalion, part of Service Squadron 12, began dredging on September 20, 1944, to provide a 32-foot channel and 29-foot berthing space. The dredging was completed by January 20, 1945.
An urgent need for pontoon equipment arose in connection with the waterfront development. To meet the demand for a floating pile-driving barge, a 6-by-12-pontoon barge was built and fitted with fair leads and anchor guide lines, 3 two-drum power winches, and a 12-inch-by-12-inch timber matting, to serve as a base on which to work a 20-ton crane. The next project was construction of a 6-by-18-pontoon barge with two propulsion units and a 75-ton fixed-boom crane to lift heavy cargo from ships and to raise small boats and landing craft out of the water. A T-shaped pontoon pier was built as a small-boat landing, and a 2-by-14-pontoon string was sunk for LCT landings.
Stevedoring operations were begun at Tinian Harbor on August 2, 1944, by CBD 1036, a detachment of half-battalion strength. The Seabees performed all transfer of cargo from vessels in the open stream to LCT's, and work parties of the Army and Marines unloaded the LCT's at the beach.
On November 19, 1944, the 27th Special Battalion, at that time only half of regular battalion strength, arrived at Tinian to handle the cargo in
the stream, while CBD 1036 took over beach operations. On January 20, 1945, CBD 1036 was absorbed by the 27th Special Battalion.
From D-Day until the completion of docking facilities in March 1945, all cargo was moved to the beach by lighters, most of them LCT's, and LCM's. Cargo-handling operations were under the supervision of an Army port superintendent. An Army port battalion of five companies shared stevedoring assignment with the Seabees.
When United States troops took Tinian, the construction forces inherited a network of roads that became the fabric of the island's road system. The general layout of the existing roads and the similarity in shape of Tinian to Manhattan Island resulted in the naming of the roads after the streets of New York.
The Japanese-built roads were too narrow for our heavy traffic, were poorly drained, and had no shoulders. Heavy trucks slid into the ditches and tracked a slippery coating of mud upon the road surface in climbing back.
The first problem was the maintenance of the 35 miles of existing roads, with the limited equipment which could be spared from high-priority airfield construction. The Japanese roads were resurfaced with 8 inches of pit-run coral, and the necessary shoulders and drainage were provided. Rainy seasons and dry seasons produced conflicting road maintenance problems. In dry weather, the roads became dusty and rough, and a continuous wetting-down with salt water was necessary. It was found advantageous to mix clay with the coral surface during this season. During the rainy season, the roads had to be bladed to the center after each rain in order to be kept passible.
As equipment became available, new road construction was pushed to the utmost. Tinian consists of several plateaus of different heights, and road construction required a great deal of blasting in order to keep the grades down for heavy-truck traffic. The roads were built 22 feet wide, with 3-foot shoulders and ditches to carry off heavy rainfall. Major roads were surfaced to 30 feet
in width to support heavy traffic. About 34 miles of new roads were constructed on the island. To solve the problem of rapidly increasing traffic on the two main north-south roads, a second 22-foot lane was constructed parallel to each road to provide dual highways.
Necessity for camp construction was considered to be of secondary importance to the completion of military installations on Tinian, once a unit had standard minimum facilities. Camps were divided into two main classes: temporary camps, of framed tents with wooden decks and screened sides, and semi-permanent camps with quonset huts for Navy and aviation personnel and prefabricated wooden barracks for Army personnel. Both types of semi-permanent buildings were allocated on the basis of 20 enlisted men or eight officers per building.
One difficulty in camp constructions was the clearing of cane fields, but removal of the valuable thin top-soil, with the roots, allowed erosion from heavy rains and winds. Bulldozers had piled both cane and top soil in huge pits that had to be removed by clamshell and truck. The Seabees, therefore, started using a sheepsfoot roller for clearing, removing the cane later, by hand. This method left enough roots in the ground to prevent extensive erosion.
Another problem was the building of mess halls and similar facilities for large units, with only 20-by-56-foot quonsets supplied. It was found that by using concrete floors, 20-foot-wide quonset floor beams could be used for roof trusses and the quonsets stretched to both 34-foot and 39-foot widths where large buildings were necessary.
The development of housing on Tinian involved camps for more than 12,000 Seabees, 13,000 other naval personnel, and 21,500 Army personnel.
The first medical facility on Tinian, a 100-bed tent hospital, was completed in September 1944. This served as the only hospital on the island for military personnel until the completion of the 600-bed Navy Base Hospital 19, in early December. Quonset huts, modified where required to suit operational needs, were used. Rearrangement of floor space increased the capacity to 1,000 beds. A 600-bed hospital of similar design was completed for the Army in March 1945. A 1,000-bed hospital was made available in June, with the reconversion of the camp area vacated by the 135th Battalion, which moved to Okinawa. On V-J Day, construction was nearing completion on a 4,000-bed hospital on the South Plateau.
General supply facilities for Tinian were of three types: those for the garrison forces; those for general Navy supply activities; and those for the Sixth Brigade, which handled construction supplies.
In early August 1944, the 92nd Battalion was assigned the layout and construction of the Seventh Field Depot for the Marines. The project, which included camp facilities for a Marine quartermaster battalion and the improvement of 300,000 square feet of open storage space, was completed early in November. In December, the 18th Battalion began the reconstruction and expansion of the depot, then designated as the quartermaster depot of the Army garrison forces. The completed depot consisted of three camps, 386,000 square feet of warehouse storage, two million square feet of surfaced open storage, and about 63,000 cubic feet of refrigerated storage.
For the naval supply depot, the Seabees erected seven steel arch-rib buildings and provided 16,000 square feet of storage space in frame warehouses.
A spare parts depot and an ABCD Annex were constructed for the 6th Brigade. The spare parts depot, consisting of six steel arch-rib buildings and one quonset hut, was completed in January 1945. By early May, seven steel arch-rib buildings, two quonsets, and a surfaced storage yard with 575,000 square feet of space had been constructed for the ABCD Annex.
In September 1944, the first ammunition storage dump of 11 revetments was constructed. Access roads were developed on the basis of existing roads. Expansion of this facility to include 254 coral-surfaced revetments, 25 by 75 feet, and almost 14 miles of main and secondary roads, undertaken in November 1944, was completed in February 1945.
On January 28, 1945, work was started on an additional bomb dump of 20,000-ton capacity, in an area near West Field. Work progressed slowly because of limited equipment; the 468 revetments were not finished until early summer of 1945.
In February 1945, the Seabees met a three-week deadline in the construction of an aerial mine assembly and storage depot. The project involved the construction of two 40-by-200-foot quonset huts with concrete decks, surrounded by a 12-foot earth revetment on three sides; two 20-by-50-foot quonset magazines with concrete decks and an earth cover;
twelve 30-by-40-foot ready storage revetments; and about one miles of 20-foot, coral roadway.
Tinian, though it contains not a single stream and has only one small fresh-water lake, is an island rich in water. The average yearly rainfall is in excess of 100 inches, and the porous coraline structure of the island permits the rain water to filter into the ground with very little runoff. The Japanese had developed a well-and-reservoir system, with the necessary pipelines to serve the Tinian Town area.
After the island was secured, the Seabees assumed the development and control of the water supply. Purification units were set up at four small shallow wells in the Marpo region, where the water was filtered and chlorinated. These wells, in addition to Hagoi Lake, provided sufficient water, with rationing.
The Seabees rehabilitated and extended the existing Japanese pipeline from the reservoir. Well drilling was undertaken, and, and the water system was eventually composed of 17 deep wells. Marpo well, Tinian Town well, and Hagoi Lake, providing 20 gallons of water, per man, daily. With the increased development of water sources during August, it was no longer necessary to ration water.
The water supply eventually included a skimming trench in Marpo Valley, designed to produce 1,800,000 gallons per day. The service group camps and shops at north Field were supplied from two wells in that vicinity. The island system was designed for 30 gallons per man per day.
To provide drinking water, food, clothing, and shelter for the civilians held in custody at Camp Churo, reliance was placed on what facilities the Japanese had left.
Using Japanese four-by-four timber taken from damaged farm and village buildings, the Seabees supervised the native laborers in the construction of tarpaulin shelters for initial housing. As more materials were brought in by salvage crews, the tarpaulin shelters were replaced by wood-frame and corrugated-iron roofed sheds.
A 100-bed civilian hospital, constructed largely of salvaged material, was completed in September 1944. A 100-bed quonset-hut hospital replaced this initial hospital in April 1945.
Captured Japanese civilians, who knew the location of food supplies, were assigned to food salvage details. The existing food supply was supplemented by American food and by extensive agricultural development. When firewood supplies on the island
showed signs of exhaustion, the Seabees improvised a diesel-oil stove for cooking, using cement and salvaged fire-brick, with burners made of salvaged scrap pipe and tubing.
The capture of Iwo Jima, halfway between Saipan and Tokyo, not only eliminated a base from which the Japanese could attack United States installations in the Marianas, but, more significantly, provided a site for the development of airfields to support the operations of fighters escorting Superfortresses in their missions over Japan and to afford emergency landing fields for crippled B-29's returning from the raids.
Iwo Jima, the largest island of the Volcano group, is about five miles long and two and one-half miles wide at its broadest point. The most prominent feature is Mt. Suribachi, a volcanic cone rising to nearly 550 feet at the southern end of the island. The northern half of the island forms a broad dome, with maximum elevations of 340 to 387 feet. Iwo has enough flat land in its 8 square miles for the construction of airstrips. The entire shore is rugged and precipitous, with few good landing-beaches. The Japanese took advantage of the terrain and developed Iwo Jima into an air base, two fields being operational and a third under construction at the time of the American assault. The southernmost field had two strips, 5,025 and 3,965 feet long, respectively. Two runways, forming an X, had been built to 5,225 and 4,425 feet in length, near the center of the island. A third strip, 3,800 feet long, had been started farther north. These three fields, the main objective of the assault, became the nucleus for the development of an advance air base for United States aircraft.
The assault on Iwo Jima was initiated on February 19, 1945, by the Fifth Amphibious Corps and the Third, Fourth, and fifth Marine Divisions. Three Seabee units, the 31st, 62nd, and 133rd battalions, were assigned to the Marines during the assault, to act as shore parties and to start work on the airstrips at the earliest possible moment.
The Marines went ashore on the southeastern beaches of Iwo Jima, meeting relatively little resistance. However, the enemy, taking advantage of the hilly terrain, soon concentrated extremely heavy artillery and mortar fire against the Marine positions. By the evening of D-day, the marines had cut across the narrow isthmus to the west shore of the island, isolating the southern airfield, which was captured the following day. By February
26, the northeast-southwest Japanese runway had been made operational by the Seabees and was in use by observation planes.
The Marines continued their painful advance toward the northern tip of the island and by March 3 had captured all three airfields. On that date, transports began operating from South Field to bring in much-needed supplies and to evacuate the wounded. Effort was concentrated on the rehabilitation of the northeast-southwest 5,225-foot strip which had been constructed by the Japanese at Central Field. By the time Iwo Jima was secured on March 16, both South and Central Fields had one operational strip, and 50 Superfortresses had made emergency landings on their return from great incendiary raids over Japan.
With the close of the assault phase of operations, attention was turned to the execution of plans for the development of Iwo Jima as an important air base. The Ninth Construction Brigade was organized for this purpose. The Eighth Regiment, consisting of the 8th, 90th, 95th (Section Two), and the 23rd Special Battalions, and the 41st regiment, composed of the assault battalions, made up the brigade.
Initial plans called for the development of three airfields, to be known as South, Central, and North Fields, on the sites of the existing Japanese strips. The 5,025-foot strip at South Field was to become a 200-by-6,000-foot fighter strip. The longer runway at Central Field was to be extended to 8,500 feet for B-29 operations, and a similar strip was to be constructed parallel to it. In addition, the second strip at Central Field was to be extended to 6,000 feet. North Field, where the Japanese had only started construction, was to have one 200-by-5,000-foot strip for fighter operations.
At South Field, the temporary strip was rebuilt and additional taxiways, shops, and service areas were constructed while the field was in constant operation. On April 7, 1945, fighters took off from South Field to form the first land-based fighter escort for B-29's on a strike against the Japanese homeland. By July, the runway had been extended to 6,000 feet and had been surfaced with emulsified asphalt. Also constructed were 7,950 feet of taxiways and 258 hardstands.
By July 7, 1945, the first B-29 strip at Central Field had been paved to 8,500 feet and placed in operation. During the day, 102 B-29's, returning from a raid on Japan, landed on the field. Several sub-grade failures occurred in the construction because of ground water and soft spots in the sub-grade. In some places the paving sealed off steam which had been generated below the surface. When the steam condensed, the sub-grade became saturated. At one time, poor subsoil under the paving made it necessary to remove about 1,500 feet of crushed stone and sub-grade. By July 12, the B-29 strip had been completed and paved for a length
of 9,800 feet. The east-west runway was developed into a fueling strip, 6,000 by 570 feet, with 60 fueling outlets. The second B-29 strip had been graded to 9,400 feet by V-J day, and was left unpaved.
Virtually the entire job at North Field was new construction in rough terrain which consisted principally of consolidated volcanic ash. The initial portion of the work in preparing the sub-grade for the strip entailed the moving of about 200,000 cubic yards of rock and volcanic ash. Seabee construction was stopped on April 27, and the project was turned over to an Army Engineer battalion for completion. By V-J day a strip 6,000 feet long, had been graded and was paved to 5,500 feet; 10,000 feet to taxiways had been graded; and 129 fighter hardstands had been provided.
All facilities on Iwo Jima were constructed to support the air base. Main projects were tank farms, water-distribution system, roads, hospitals, storage areas, and waterfront facilities.
A temporary tank farm, consisting of four 1,000-barrel tanks -- two for aviation gasoline, one for motor gasoline, and one for diesel oil -- was ready for operation on March 16, 1945. Dismantling of this farm began when the permanent farms were placed in operation. The permanent tank-farm system consisted of two central farms, called East and West Farms, and small farms at each of the three airfields. Small installations provided 1,000 barrels of aviation gasoline for South Field; 6,000 barrels for Central Field; and 6,000 barrels for North Field. The East Tank Farm, for aviation gasoline only, had a capacity of 80,000 barrels. West Farm facilities consisted of 160,000 barrels for aviation gasoline, 50,000 barrels for motor gasoline, and 20,000 barrels for diesel oil.
All unloading of cargo at Iwo Jima was across the beaches. Berthing was later developed at both eastern and western beaches, the latter proving much more satisfactory. Stevedoring was extremely difficult because of the heavy surf, bad weather, and sand conditions on the beaches. During the assault, marston mat was extensively used to make possible the landing of wheeled vehicles.
Harbor development consisted of a breakwater and blockships on the east side of the island and a small boat pool on the west side. A storm wrecked the blockship breakwater, and no further attempt was made to provide seaward protection for ships.
A project of high priority was the provision of a water-supply system. There are no perennial streams on Iwo and the water table lies at a considerable depth near the center of the island. A fresh-water lens, extending about 9 feet above sea-level, had formed, and wells were drilled to secure water from this lens. The Japanese had dug 14 wells, eight of which were used in the development of the water system. In addition, the Japanese had paved catchment-areas which were drained into cisterns excavated in the soft rock. The runoff from the two completed airfields had been stored in masonry and concrete reservoirs, which were repaired by the Seabees and became the basis of the water system. By V-J day, the system was only
half finished, with 58 small stills and eight drilled wells.
Establishment of storage areas for the ordnance, quartermaster, medical, engineering and chemical warfare departments involved the construction of quonset huts, frame buildings, and open-storage areas, as well as 27,000 cubic feet of refrigerated storage space.
Housing and messing facilities for 37,000 officers and men were set up, in addition to the individual battalion camps. Tents were used for living quarters, and quonset huts were provided for headquarters and mess halls. Medical facilities were provided at the 38th Field Hospital, the 41st Station Hospital, and the 232nd General Hospital, with a total capacity of 1,250 beds. There were also 105 beds in Navy dispensaries.
The first Seabee road construction involved the hacking of a road up Mt. Suribachi to install radar equipment. The Japanese had made no attempt at this construction. After a demolition team had cleared the terrain of mines and booby traps, a bulldozer blazed a trail to the top, and within twelve days, graders, scrapers, and dump trucks had completed the road.
To link the various activities on Iwo Jima, 20 miles of primary and 40 miles of secondary roads were constructed.