HEAVY SINKINGS ON EAST COAST OF UNITED STATES
JANUARY 1942 - SEPTEMBER 1942
4.1 U-BOAT OFFENSIVE
THE GERMANS started this period with about 200 ocean-going U-boats and new U-boats were being commissioned at the rate of about 20 a month. Admiral Doenitz was therefore able to maintain a large-scale U-boat offensive over widely spread areas throughout this period. The average number of U-boats at sea in the Atlantic increased steadily from 22 in January 1942 to 93 in September 1942. In addition, there were about 20 U-boats in the Mediterranean and about 20 available for operations in the Barents Sea. These U-boats were used in a specific effort to cut supply lines to Allied forces in Libya and Russia. Japan, at the start of this period, had about 75 U-boats which operated in the Pacific and Indian Oceans.
Despite this widespread U-boat activity, the main battle continued to be fought in the Atlantic Ocean. There, during the previous period, U-boat operations against escorted shipping had been steadily becoming less and less profitable. The average yield had been reduced to about one ship sunk per U-boat month at sea during the last period. The operation against Convoy HG 76 in December 1941 had been particularly costly, as only two merchant ships were sunk as against four U-boats sunk. It was natural, therefore, after the entry of the U. S. into the war, that the U-boats, continuing their search for weak spots in the Allied defenses, headed westward for the American coast in January 1942.
The U-boats, working their way down the American coastline from the Newfoundland banks, found exactly the weak spot they were looking for. The demands of the war in the Pacific and commitments in transatlantic escort (including destroyers transferred to the British in 1940) contributed to the United States' lack of preparedness for the scale of attack launched by the U-boats on the Atlantic coast in 1942. The forces available to combat these enemy activities were relatively untrained and inexperienced. With the limited number of antisubmarine craft, both surface and air, at their disposal, the U. S. Navy was unable to start convoying coastal shipping immediately, but tried during the early months of 1942 to cover the long coastal route by patrol. This produced a number of attacks on U-boats but it failed to prevent extremely heavy losses of shipping sailing unescorted along the coast.
U-boat activity in the West Atlantic began on January 12, 1942, when the first sinking west of 60° west longitude occurred. A force of about 20 U-boats began to operate off the Atlantic seaboard of the United States and in the coastal area of Nova Scotia and Newfoundland. These U-boats were rather selective in their choice of targets, preferring tankers and larger cargo ships and avoiding convoys. As long as worth-while targets abounded in the form of unarmed and unescorted ships, the U-boats kept clear of escorts, as even minor damage might well have prevented their return to distant bases.
The U-boats inflicted their heaviest losses in January in the Eastern Sea Frontier, sinking 14 ships of about 100,000 gross tons with a large proportion of the losses occurring at focal points of shipping such as Cape Hatteras, North Carolina, and Hampton Roads, Virginia. About 50,000 gross tons of shipping were sunk by U-boats in each of the Northwest Atlantic, Canadian Coastal, and Bermuda Areas. There was comparatively little activity in the remainder of the Atlantic, but Japanese U-boats sank 50,000 gross tons of shipping in the Pacific and Indian Oceans. The total losses for the month, 61 ships of 324,000 gross tons sunk by U-boats, were higher than those in any month in the previous period.
The situation became much worse in February 1942 with the world-wide shipping losses to U-boats reaching a new high for the war as 82 ships of 470,000 gross tons were sunk. About 90 per cent of these losses occurred in the U. S. Strategic Area as the number of U-boats operating in the West Atlantic increased and U-boat activity spread further south with ships being sunk off the coast of Florida and in the Caribbean Sea. Tanker losses continued to be severe, with the
tanker traffic to and from the West Indian and Venezuelan oil fields being an obvious objective of the U-boats. This was shown by an attack carried out by several U-boats on February 16 on six tankers off Aruba and in the Gulf of Venezuela, five being sunk and one seriously damaged.
During March the U-boats continued the same tactics with increased success as they sank 94 ships of 532,000 gross tons. The Eastern Sea Frontier continued to be the most active area, with over 150,000 gross tons of shipping sunk there by U-boats. Possibly by way of diversion, a group of U-boats operated in the Freetown Area, sinking over 50,000 gross tons there.
The one encouraging feature of the month's operations was the first successful attacks on U-boats in the U. S. Strategic Area. Two U-boats were sunk in March as a result of attacks by U. S. Navy aircraft in the Canadian Coastal Zone. On April 15, USS Roper sank U-85 off Cape Hatteras, picking up 29 bodies, for the first confirmed sinking of a U-boat off the U. S. coast. The number of attacks on U-boats in the U. S. Strategic Area had increased from about 15 in January to about 60 in April.
These more effective countermeasures probably played some part in causing a small decrease in shipping losses in April, but a more important factor was the temporary suspension of sailings in certain areas. U-boat activity spread to the Brazilian Area during April as three ships were sunk off the north coast of Brazil, probably by Italian U-boats.
In the middle of May 1942, the U. S. Navy was able to start convoying shipping along the east coast. The effect of the institution of these convoys was immediately apparent. The U-boats avoided escorted shipping and the tonnage sunk by U-boats in the Eastern Sea Frontier in May dropped to 23,000 gross tons. Logically enough, the U-boats sought out the remaining soft spots, where unescorted traffic had to pass through focal areas, and operated actively off the mouth of the Mississippi and in the Yucatan Channel between Cuba and Nicaragua.
Although the average number of U-boats at sea in the Gulf Sea Frontier in May 1942 was only about four, these U-boats sank 41 ships of 220,000 gross tons there during the month, an all-time high for sinkings by U-boats in any area. The average number of ships at sea in the Gulf Sea Frontier was about 75, so the average life of a ship at sea at that time was less than two months at that rate of sinkings.
Sinkings in the Caribbean Sea Frontier also increased, reaching about 170,000 gross tons in May. Consequently, despite the decrease in the Eastern Sea Frontier, the losses in the U. S. Strategic Area reached a peak of 116 ships of 567,000 gross tons sunk by U-boats in May. The world-wide shipping losses to U-boats also reached a new high for the war as 124 ships of 604,000 gross tons were sunk during this month. The number of attacks on U-boats in the Western Atlantic showed a promising increase, however, and two U-boats were sunk by U. S. Coast Guard cutters, one in the Eastern Sea Frontier and one in the Gulf Sea Frontier.
The world-wide shipping losses to U-boats reached their highest point in the war in June 1942, when 141 ships of 707,000 gross tons were sunk. The bulk of the increase over the figures for May was accounted for by increased activity by Japanese U-boats, which sank 70,000 gross tons in the Indian Ocean, mostly in the Mozambique Channel. The shipping losses in the U. S. Strategic Area were about the same as in May, falling off in the Gulf Sea Frontier but continuing to increase in the Caribbean and Panama Sea Frontiers. Mines were laid in the Chesapeake, causing several casualties in June. This mine-laying may have represented the first effort of one of the 1600-ton mine-laying U-boats introduced by Germany at about that time. Over 100 attacks were made on U-boats in the U. S. Strategic Area in June; three of these attacks resulting in sinking U-boats.
During July 1942 the convoy system on the east coast of the U. S. was greatly extended, with the bulk of shipping traveling in convoy. This increase in the number of convoys and an improvement in the strength of escorts were probably mainly responsible for the general reduction in sinkings of shipping throughout the U. S. Strategic Area. Only 230,000 gross tons of shipping were sunk by U-boats in the U. S. Strategic Area in July, less than half the amount sunk in June; this, despite the fact that the average number of U-boats at sea in the U. S. Strategic Area in July was about 45, higher than in any previous month. Increased aircraft patrols and better cooperation between surface and air units also contributed materially to this reduction of U-boat effectiveness in the West Atlantic. Another significant factor was the increase in the number of U. S. craft available for antisubmarine warfare; 134 ships in July as compared to 68 in April and 580 planes in July as compared to 350 planes in April. The increased effectiveness
of U. S. countermeasures is also illustrated by the fact that the number of U-boats lost in the U. S. Strategic Area reached a new high in July as seven were sunk, two in Eastern Sea Frontier, one in Gulf Sea Frontier, two in Panama Sea Frontier, and two in the Northwest Atlantic Area.
As a result of the greatly reduced losses in the West Atlantic, the world-wide shipping losses to U-boats dropped to 94 ships of 472,000 gross tons in July 1942. However, increased losses were suffered in the Freetown and Azores Areas with over 50,000 gross tons sunk by U-boats in each of these areas. Heavy losses were also suffered in July in the Barents Sea Area, where ten ships of 62,000 gross tons were sunk by U-boats from Convoy PQ 17 heading for Russia. In addition, 13 ships were sunk from this convoy by enemy aircraft. The convoy had been ordered to scatter when southeast of Spitzbergen to reduce losses from the enemy surface craft attack then apparently pending.
The shipping losses to U-boats increased slightly in August to 108 ships of 544,000 gross tons, still well below the record highs established in May and June 1942. This increase was due entirely to increased activity in the U. S. Strategic Area, where the losses mounted again to 84 ships of 407,000 gross tons sunk by U-boats. Over half of these losses occurred in the Caribbean Sea Frontier, where the main sore spots were the eastern approaches to Trinidad and the Windward Passage area. A group of about five U-boats achieved considerable success, especially against tankers, east of Trinidad. Twenty of the 23 ships sunk there were sailing independently. In the Windward Passage area 14 ships were sunk from convoys running between Key West and Trinidad and between Panama and Guantanamo. The activities of probably two U-boats off the Brazilian coast resulted in seven sinkings and brought Brazil into the war on the side of the United Nations. The coastal waters of the Atlantic from Nova Scotia to the tip of Florida were free from attacks by U-boats during the entire month of August.
The other significant trend of the month's operations was the resumption of large-scale attacks on the transatlantic convoys. In view of the reduced effectiveness of U-boats in the Eastern and Gulf Sea Frontiers, due to the start of convoying and the heavy aircraft coverage, it was natural that the U-boats would resume their attacks on the transatlantic convoys, especially in areas in the North Atlantic out of the range of land-based Allied aircraft. Over 20 ships of about 120,000 gross tons were sunk by U-boats in the Northwest Atlantic Area in August. The heaviest losses were suffered by Convoy SC 94, which lost 11 ships as a result of U-boat attacks.
In these attacks on convoys, the first indication of the presence of U-boats was often an HF/DF bearing, and these were of great assistance to escort commanders in appreciating the subsequent situation. Shipborne 10-cm radar (SG and Type 271) also proved a most efficient detector at night, and the quick action taken by escorts in many cases thwarted night attacks. This apparently influenced some of the U-boats to temporarily abandon their tactics of night surfaced attack and to attack submerged in daylight. As many as five ships were torpedoed by one salvo on a day attack, and to lessen the chance of such an event recurring instructions were issued in the third week of August to open out the distance between the columns of a convoy to about 1000 yards by day as well as by night.
The number of U-boats destroyed during August reached a new high for the war as 20 were sunk or probably sunk, 12 in the Atlantic, five in the Mediterranean, and three in the Pacific. Two U-boats were sunk by escorts of Convoy SC 94 and a U-boat was sunk in the Caribbean Sea Frontier for the first time. U-464, sunk by a U. S. PBY plane southeast of Iceland, turned out to be one of the new 1600-ton supply U-boats. These were used to refuel other U-boats at sea and thereby enabled them to extend their cruises. These supply U-boats were intended to stay at sea for as long as six months.
At the end of August, the coastal convoy system was further extended and New York included as one of the ports in the system. In September, New York also became the main western port for the transatlantic convoys, with HX and SC convoys beginning and ON convoys ending their passages there. Another new development in September was the establishment of a temporary reinforcing group whose primary objective was the destruction of U-boats rather than the immediate defense of shipping. This group consisted of ten British escorts.
The shipping losses to U-boats decreased slightly in September to 99 ships of 496,000 gross tons. The principal areas of attacks on shipping were in the eastern approaches to Trinidad and in the area to the north and south of the Equator between Freetown and Ascension Island. There was also considerable
activity along the convoy routes in the Northwest Atlantic as well as in the Gulf of St. Lawrence.
In the Northwest Atlantic Area, U-boats sank 20 ships of 110,000 gross tons. The chief sufferer on the North Atlantic convoy routes was ON 127, with which five or six U-boats were in contact for four days in succession. In the course of these attacks, two of which were made in daylight, 11 merchant ships and one escort were torpedoed, four of the ships managing to reach port.
The two North Russian convoys had to fight. their way through incessant U-boat and aircraft attacks, losing 16 ships in all, eight to U-boats. Six very promising attacks were carried out by the escorts who were assisted by Swordfish aircraft from HMS Avenger. This was the first operation in which this type of escort carrier had taken part. The losses to U-boats in the Caribbean Sea Frontier in September 1942 were 27 ships of 130,000 gross tons, considerably less than in August. A notable feature of the operations around the Trinidad Area was the sinking of ten ships engaged in the valuable bauxite trade. With the tremendous increase in shipping to and from the South Atlantic, the Trinidad Area had become one of the largest shipping focal points in the Western Hemisphere. U-boat activity had increased accordingly and was highly successful at first. Lack of suitable long-range surface and air craft restricted the distance that east-bound convoys could be escorted from Trinidad. Beyond the dispersal points the U-boats had good hunting.
Aircraft available in the Trinidad Area, especially the RAF Squadron 53 (Hudsons), were utilized to the utmost and reinforcement aircraft from other areas, including a specially trained "Killer" group of U. S. Army Air Force B-18's, were ordered into the area. Emphasis was placed on offensive operations, using sweeps over most likely U-boat locations and routes along which convoys passed. The results were rather encouraging in September as one U-boat was sunk and several other promising attacks were made. The situation became somewhat eased after September as the number of U-boats in the area started decreasing. Therefore, in just over nine months from their entry into World War II, the United States, by the institution of escorted convoys and the provision of air cover and air patrols, had achieved a high degree of immunity from U-boat attack in their coastal waters.
4.2 COUNTERMEASURES TO THE U-BOAT
In January 1942, the U-boats transferred their attention from the transatlantic and East Atlantic convoys to the unescorted shipping in the West Atlantic. This is reflected in the fact that only 10 per cent of the shipping sunk by U-boats during the first six months of 1942 was in convoy when sunk. This proportion increased again to about 30 per cent during the period July to September 1942 when the bulk of U. S. coastal shipping was being convoyed and the U-boats were attacking the transatlantic convoys again.
It was realized during the early months of the war that convoying was the only solution to the heavy losses off the Atlantic Coast. However, the U. S. Navy, due to its commitments in transatlantic escort and in the Pacific, did not have enough escorts to start the convoying of coastal shipping at the beginning of 1942. To provide additional forces, 24 British antisubmarine trawlers were allocated for service on the American coast and ten British corvettes were turned over to the U. S. Navy. Further, the whole system of transatlantic escort was recast and all antisubmarine forces (U. S. Navy, Royal Canadian Navy, and Royal Navy) were pooled in a single cross-Atlantic convoy scheme. This resulted in a certain economy and released a limited number of U. S. destroyers.
With the forces thus available and with the increased production of antisubmarine ships in the United States, it was possible to start convoying in the Western Atlantic in May 1942. Coastal convoys between Norfolk, Virginia, and Key West, Florida, started running on May 14. By opening up the transatlantic convoy cycle, the British were able to divert enough forces to the Caribbean to start convoys, mainly for tankers, over the Trinidad-Halifax and Aruba-Curacao-Trinidad routes.
During July, the convoy system on the cast coast was greatly extended, with convoys running between Trinidad and Key West by way of Curacao and Aruba. Convoys were instituted between Panama and Guantanamo to connect with the other convoys. Convoys were also started in the Gulf of Mexico and the Gulf of St. Lawrence.
At the end of August, convoys running in both directions between Curacao and Halifax and between
Key West and Trinidad were discontinued, as were also the convoys between Hampton Roads and Key West. A new convoy system was started with convoys running between New York and Guantanamo [NG and GN], and between the latter port and Trinidad by way of Curacao [GAT and TAG]. Convoys were also started between New York and Key West [NK and KN].
During the five months from May through September 1942 about 1800 ships were convoyed monthly in the U. S. coastal convoys and only about 12 of these ships were sunk monthly by U-boats for a loss rate of less than I per cent per trip. During the first nine months of 1942, about 1000 ships were convoyed monthly in ocean convoys and about 15 of these ships were sunk monthly by U-boats for a loss rate of about 1i2 per cent per trip. (It should be considered that the average voyage for these convoys is considerably longer than for the coastal convoys.) The convoy run to and from Russia was particularly hazardous during this period, with about 34 ships sailing monthly and about three of these being sunk monthly by U-boats for a loss rate of about 9 per cent per trip. In addition, these convoys suffered considerable losses from enemy air and surface craft attack.
The effect of convoying in reducing shipping losses is clearly illustrated by the experience in the U. S. Strategic Area during the first nine months of 1942. There were about 600 ships at sea in this area throughout this period. During the first six months, before extensive convoying of coastal shipping had started, only about 40 per cent of the shipping was in convoy. There were, on the average, about 30 U-boats at sea in this area during the first six months and each U-boat was sinking about 2.7 ships a month. About 20 per cent of the independent shipping and about 4 per cent of the convoyed shipping were sunk each month by U-boats.
During the next three months, after extensive convoying of coastal shipping had started, about 80 per cent of the shipping was in convoy. The average number of U-boats at sea in this area had increased to about 50, but each U-boat was only able to sink about 1.4 ships a month, about half as much as during the first six months. Thus, despite the fact that the loss rates for both independent and convoyed shipping had increased (about 33 per cent of the independent shipping and about 6 per cent of the convoyed shipping were sunk monthly by U-boats) during the last three months of this period, the efficiency of the average U-boat in sinking ships was halved. This was mainly due to the fact that about 40 per cent of the shipping was exposed, during the latter three months, to the much lower loss rate experienced by convoyed shipping instead of to the high loss rate experienced by independent shipping.
Another consequence of the shift from independent to convoyed shipping is the increased danger which the U-boat faces when he attacks a convoy. Only about 1i3 U-boats were sunk monthly in the U. S. Strategic Area during the first six months of 1942, while 41//3 were sunk monthly in the same area during the next three months, most of them by forces escorting convoys.
At the beginning of 1942, the U. S. Navy sent out all available planes and blimps to battle the U-boats along the coast. They were helped by the First Bomber Command, initial Army Air Forces contribution, which was activated in December 1941. The Army planes patrolled and escorted under the operational control of the Navy. A second Army Air Forces unit broke into the picture in June 1942. This was the Seasearch-Attack Development Unit [SADU], based at Langley Field, Virginia, and assigned a combination mission: (1) to develop tactics and techniques for using antisubmarine devices, and (2) to conduct general seasearch. SADU had two British loaned B-24's (Dumbos I and II) . In these had been installed two early British microwave sets known as DMS-1000 and equipped with the first airborne Plan Position Indicator [PPI] scopes. In addition to the Army and Navy flying, there was also patrolling by the Civilian Air Patrol [CAP], mostly within 100 miles from shore.
The flying hours by U. S. Army and Navy aircraft in the Eastern Sea Frontier increased from about 5000 hours in January 1942 to a peak of about 25,000 hours in July 1942. In the Gulf Sea Frontier, only about 7000 hours were flown in May 1942, when sinkings of ships were at their peak, as compared to 12,000 hours in July 1942. In both of these sea frontiers, the number of U-boats at sea decreased rapidly after July 1942. In the Caribbean Sea Frontier, the number of flying hours increased from about 5000 in April 1942 to almost 10,000 in September 1942, when the number of U-boats at sea there started decreasing. U. S. aircraft made about 30 attacks a month on U-boats during this period, varying from about 12 a
month during the first four months of 1942 to about 45 a month during the next five months. About 20 per cent of these attacks resulted in some damage to the U-boat, while only about 2 per cent of the attacks resulted in the sinking or probable sinking of the U-boat. The average height at which these attacks were made was about 150 feet. The depth bombs used were generally set for a depth of 50 feet at the beginning of this period (too deep for a surfaced U-boat) but toward the end of 1942 most of the attacks were made with settings of 25 feet. In addition, bombs were fitted with flat noses in order to reduce their forward motion under water and also to reduce ricocheting.
At about the beginning of 1942, Coastal Command aircraft had started using the 25-foot depth setting on their depth charges. The usual height at which their attacks were made was about 50 feet. Torpex-filled depth charges, which had a greater lethal radius, were introduced in April 1942. These factors produced a considerable improvement in the quality of Coastal Command attacks on U-boats. About 20 per cent of their aircraft attacks during this period resulted in at least some damage to the U-boat, while about 4 per cent of their attacks resulted in sinking the U-boat.
During the early months of 1942, when most of the U-boats were operating in the West Atlantic, Coastal Command aircraft started maintaining offensive patrols against transit U-boats. They operated both on the northern route, to the northward of Scotland, and in the approaches to the Bay of Biscay ports. During the first five months of 1942 only about 600 flying hours a month were spent on the Bay of Biscay offensive. This effort resulted in about seven sightings a month, enough to keep the U-boats submerged during the daytime.
In June 1942 Coastal Command introduced into operation about ten Wellington aircraft, fitted with the Leigh Searchlight and Mark II radar. These aircraft, operating in the Bay of Biscay, flew 190 hours in June, sighted seven U-boats, and attacked five of them. This success was achieved despite the fact that the night offensive in the Bay was considerably hampered by the presence of French fishing boats.
With the introduction of the Leigh-Light Wellington in June 1942 the scale of the Bay offensive was greatly increased, with about 3400 flying hours being put into it monthly during the period from June through September 1942. About 30 sightings (9 per 1000 hours on patrol) and 23 attacks were made monthly during this period. It is believed that 43 per cent of all U-boat transits through the Bay were sighted and that five U-boats were destroyed during those four months. The immediate reaction of the enemy to the Coastal Command offensive in the Bay was an increased effort to intercept antisubmarine aircraft, to which Coastal Command replied by sending out Beaufighters to intercept the interceptors.
4.2.3 Scientific and Technical
The Germans were fully alive to the possibilities of meter-wave radar and they were aided by the capture of a Mark II radar set in Tunisia in the spring of 1942. They accordingly concluded that radar was responsible for the night attacks in the Bay of Biscay and tests in the summer of 1942 confirmed that the transmissions were easily detected by a single receiver and aerial. Admiral Doenitz ordered the speediest equipping of all U-boats with a makeshift equipment. The aerials of wood and cable (Southern Cross Aerial) were easily made and the Paris firm of Metox turned out the R-600 receiver. The first U-boat German Search Receiver [GSR] was designed to detect meter radar and came into operation about October 1942.
Another new device introduced by the U-boats in the latter half of 1942 was Submarine Bubble Target [SBT] or "Pillenwerfer." These were tablets which were to be released by the U-boats when attacked by surface craft. The bubbles formed by the dissolving tablets produced false sonar targets which were intended to throw the attacking ships off the trail of the U-boat.
In the early months of 1942, a new form of passive defense against torpedo attacks, known as Admiralty Net Defense [AND], was being fitted to new merchant ships of speeds not less than 11 knots and not more than 15 knots. Early trials indicated that these nets would stop about 50 per cent of U-boat torpedoes fired at the ship.
In March 1912, the Hedgehog charges were made more lethal by filling them with Torpex, a new explosive which was, volume for volume, 1.7 times as powerful as TNT. About the middle of 1942, the U. S. Navy put into operation the "Mousetrap" projector, which fires a number of relatively small, fast-sinking charges equipped with contact fuzes and is suitable for installation on small antisubmarine
ships. As the light construction of these ships does not permit any great amount of deck thrust, the projector utilizes the rocket principle for launching. The projectiles are copies of the Hedgehog projectiles fitted with suitable rocket motors in the tail.
Magnetic Airborne Detector [MAD] was also developed during this period in order to enable aircraft to follow submerged submarines. This device detects the change in magnetic field produced by a submarine but its detection range is only about 500 feet.
4.2.4 Sinkings of U-boats
The number of enemy U-boats sunk during this 9-month period was 78 (50 German, 17 Italian, and 11 Japanese). Forty of the U-boats were lost in the Atlantic (21 of them in the U. S. Strategic Area), 21 in the Mediterranean, 11 in the Pacific, two in the Barents Sea, one was mined in the Baltic, and three were lost under unknown circumstances.
Surface craft continued to be the main factor in sinking U-boats in all areas, accounting for 34 U-boats (44 per cent of the total number sunk) while coordinated attacks involving both surface and aircraft accounted for another six U-boats (8 per cent). Aircraft played a significant part in sinking U-boats, for the first time, accounting for 19 (24 per cent); all of these sinkings occurred in the Atlantic and Mediterranean. Submarines were an important factor in both the Mediterranean and Pacific, accounting for 14 U-boats (18 per cent of the total).
In the U. S. Strategic Area, the main scene of U-boat activity, there were about 360 surface craft attacks made on U-boats during this period. About 12 per cent of these attacks resulted in at least some damage to the U-boat while about 4 per cent of them resulted in sinking it. A British study of 106 surface craft attacks in the North Atlantic and Western Mediterranean during this period indicates that about 25 per cent of the attacks resulted in at least some damage to the U-boat while about 10 per cent of these resulted in sinking it.
4.3 SURVEY OF RESULTS
4.3.1 From the U-boat's Point of View
This was by far the most successful period of the war for the U-boats. The total world-wide losses amounted to 878 ships of 4,587,000 gross tons sunk by U-boats (about 98 ships of 510,000 gross tons sunk monthly). The main U-boat battle continued to be fought in the Atlantic where about 90 per cent of these losses occurred. The number of U-boats lost during this period was 78 (about nine a month) so that the world-wide exchange rate was 11 ships of 59,000 gross tons sunk for each U-boat sunk.
Japanese U-boats sank 76 ships during this nine month period (48 in the Indian Ocean and 28 in the Pacific) while 11 U-boats were sunk (all in the Pacific) so that their exchange rate was about seven ships sunk for each U-boat sunk. In the Barents Sea Area, 15 ships were sunk by U-boats as against two U-boats sunk while in the Mediterranean, 17 ships were sunk as against 21 U-boats lost. Life was much more hazardous for U-boats in the Mediterranean than for those in any other area.
In the Atlantic, the main theater of activity, the average number of U-boats at sea was about 57, almost twice as many as during the previous period. These U-boats sank about 85 ships of 456,000 gross tons a month during this period, more than 2i/2 times as much as in the previous period. About 85 per cent of these losses occurred in the U. S. Strategic Area, where their main effort was directed against the weak spot off the east coast of the United States. The average U-boat in the Atlantic sank about 112 ships of 8000 gross tons per month at sea, about 50 per cent more than the corresponding figure for the previous period. However, it should be kept in mind that this sinking rate was still far below that achieved during the period front July 1940 to March 1941, when the U-boat Aces were operating and the average U-boat was sinking four ships per month at sea.
The U-boats operating in the Atlantic were relatively safer during this period than at any other time in the war. Of the 57 U-boats at sea, about 412 were sunk monthly so that the average life of a U-boat at sea reached a new high of 13 months. This meant that the average U-boat in the Atlantic, during this period, was sinking 19 ships of about 100,000 gross tons before it, itself, was sunk, the highest exchange rate of the war (about twice as high as during the previous period).
This record exchange rate was achieved by concentrating the U-boat effort in the U. S. Strategic Area, of the United States, where the defenses were rather weak and the bulk of shipping unescorted. Of the 57 U-boats at sea in the Atlantic, about 37 were
in the U. S. Strategic Area, where they were able to sink 71 ships of 375,000 gross tons a month while only 21/3 U-boats were lost monthly.
During the first half of 1942, the U-boats achieved their main successes in the Eastern and Gulf Sea Frontiers. The number of U-boats in these areas reached a peak in July 1942 when there were, on the average, eight at sea in the Eastern Sea Frontier and six in the Gulf Sea Frontier. However, by then the bulk of shipping was in convoy and surface and aircraft had each been making over two attacks a month on each U-boat. Under these conditions, the effectiveness of U-boats in sinking ships was greatly reduced, and the number of U-boats operating in these coastal regions decreased rapidly after July 1942. In the Caribbean, it was not until August 1942 that a corresponding level of attacks on U-boats was reached and the reduced effectiveness of the U-boats in sinking ships first became apparent in September 1942, when there was a peak of about 10 U-boats at sea there. The number of U-boats at sea in the Caribbean started falling off after September 1942.
It was natural, therefore, that as the combination of convoying and heavy air coverage reduced the effectiveness of U-boats along the East Coast of the United States, the U-boats would look for other weak spots in the Allied defenses. The most likely looking spot was the "gap" in the Northwest Atlantic Area where the U-boats could operate against the vital transatlantic convoys in a region outside the range of Allied air cover. The number of U-boats in this area had increased from about seven during the first half of 1942 to 14 in August and September while the shipping losses to U-boats in the Northwest Atlantic Area had mounted to over 100,000 gross tons in each of these months. It seemed likely that the crucial battle of the U-boat war would be fought against these convoys in the North Atlantic during the next period.
The Germans were in an excellent position to conduct an intensive U-boat campaign at the end of September 1942. The number of ocean-going U-boats available had increased from about 200 at the beginning of 1942 to about 350 at the end of this period. This was accomplished by commissioning about 200 new U-boats while only 50 were lost. In addition, many of the new U-boat commanders and crews had gained considerable experience and confidence as a result of their successful operations in the West Atlantic.
4.3.2 From the Allies' Point of View
Total shipping losses from all causes of the Allied and neutral nations reached the highest level of the war during this period, amounting to 700,000 gross tons a month, almost twice as high as during the previous period. Fortunately, the building rate of new shipping was also greatly increased, averaging about 515,000 gross tons a month. This increase reflected chiefly the great expansion in U. S. construction of shipping from less than 100,000 gross tons in January 1942 to almost 700,000 gross tons in September 1942. Consequently, the net monthly loss of shipping was only about 185,000 gross tons, slightly less than during the preceding period.
Of the 700,000 gross tons of shipping lost monthly, about 655,000 gross tons were lost as a result of enemy action. U-boats accounted for 510,000 gross tons a month (about 78 per cent of the total lost by enemy action), a much higher proportion than in the past. Monthly losses to enemy aircraft dropped to 67,000 gross tons (10 per cent of the total). Monthly losses to enemy surface craft were about 39,000 gross tons, while the monthly losses to mines were only about 11,000 gross tons.
The total shipping available decreased from about 33,300,000 gross tons at the beginning of 1942 to about 31,600,000 gross tons at the end of this period. Particularly serious was the heavy destruction of tankers during this period, 190,000 gross tons lost monthly as compared to 70,000 gross tons constructed monthly. The size of the tanker fleet declined by over 1,000,000 gross tons, or about 10 per cent of its size at the beginning of 1942.
The number of ships suitable for ocean escort, available to the Allies, increased from about 670 at the beginning of 1942 to 745 at the end of September. This was due mainly to an increase of about 60 in the number of destroyers. Twelve new auxiliary aircraft carriers were also completed during this period. However, the gravity of the U-boat situation at the end of this period resulted in a sizeable expansion in the construction program for 1943, with the U. S. Navy expecting to produce over 500 escort ships, more than half of which would be destroyer escorts [DE], designed especially for convoy escort and antisubmarine warfare.
Although the Allies had suffered extremely heavy losses in the Western Atlantic during this period, convoying and aircraft had succeeded in driving the
U-boats out of these coastal regions by the end of this period. The main problem facing the Allies during the next period was that of maintaining the flow of war material from the United States to England, in particular, that of assuring the safety of the North Atlantic convoys. It was becoming increasingly apparent that, although the defeat of the U-boats would not, of itself, win the war, the Allies could not possibly win the war without first defeating the U-boats.
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