The 1.1" Machine Gun

Chapter IV

a. Early History

The 1.1 pain was designed as a weapon to be used against dive and horizontal bombers and as such supplement the defensive characteristics of the caliber .50 machine gun. The first definite action in this direction took place on October 11, 1928, when the Chief of the Bureau announced a meeting of a Special Board on Naval Ordnance for October 17 to consider and submit a plan for the development and test of a machine gun of 1" or greater.[1] As a result of this and successive meetings, the decision was made to develop a 1.1" machine gun. On December 13, 1923, Mr. C.F. Jeansen, a Bureau Engineer, began an investigation of the



weight of ammunition for the gun and in March 1929 Mr. Burk and Mr. Chadwick, likewise Bureau Engineers, were designated to design the gun mechanism.

The round as finally adopted weighed 2 pounds and employed a .92 pound percussion-fuzed projectile. The design of the gun mechanism was completed in 1930 and tests on the initial models were carried out in March, April and May 1931. The tests, at which a cyclic rate of 90 r.p.m. was obtained, were characterized by primer blow backs, misfires and stuck cases as well as magazine and cradle difficulties. During the next two years these faults were corrected and the cyclic rate increased to 140. The design was turned over to the Naval Gun Factory for production in 1934. It is interesting to note that work on the gun was financed not from regular Navy
appropriations but from funds supplied through the National Industrial Recovery Act.[2]


Since the 1.1" projectile was explosive only on contact and it was desired to obtain the same volume of fire as with the .50 caliber gun, capable of a rate of 550-600 r.p.m., a quadruple mount was developed. The weight and reactions involved were thought to preclude a free swinging mount. Elevating, training and traversing gear were built into the mount and power operation for all three elements was provided. The third axle of motion was incorporated as there was a strong feeling that a technique of vertical (90°) diving would be developed and mounts with only two axes of motion could not cover such an attack. This addition, of course,added considerable weight to the mount.[3] Open sights with conventional sight setting were supplied and a target designator system in train and elevation provided. The first mount was completed in April 1935.

The issue of the 1.l" assembly for service test



and use was hurried to satisfy persistent demands for a more satisfactory weapon than the .50 caliber machine gun. The 1.1 was accordingly, perhaps in error, placed in service as soon as it was proved operable at the Naval Proving Ground and without the thorough testing that usually preceded the issue of a new type weapon. It was an interesting fact that the gun mechanism placed in service was essentially the one laid out on the drafting board. Several experimental models were not made. More time in experimental testing would have resulted in a better final design.

The assembly was well, received at first, but due to the inability to obtain the desired percentage of hits against towed sleeves, then in use as targets, it soon lost favor. As with the .50 caliber machine guns excessive vibration was stressed, with the added complaint of smoke interference, to reduce vibration, broad steel stiffening plates were placed on each side of the mount between the carriage and the base, and for new construction a complete new



design was adopted which Increased the diameter of the foundation, the width of the carriage, and stiffened parts of the mount.[4] In a further effort to improve performance the complicated traverse feature was locked out, directors were added, and an explosive projectile perfected. As firing progressed it became apparent that the guns were really doing what they were originally designed to do--a suitable pattern size and density of projectiles in the pattern was obtained, and the pattern was readily centered on a point. Improvements in the l.l", however, were not the means of stopping aircraft of improved design. It was realized that dive bombing and glide bombing had achieved a substantial advantage over our antiaircraft defense, and that the answer to the problem lay in the increase of the caliber of our heavy machine guns.[5] After careful investigation the Bureau adopted the 40mm




machine gun (Bofors) to replace the 1.1". However, procurement of the 1U1 was continued until the production and installation of the new gun were well underway.

b. Production

1. Guns and Mounts.

The 1.1" program, completed in December 1942, Involved the procurement of only 823 assemblies and an expenditure of approximately $45,000,000--a relatively Insignificant total in both numbers and cost as compared with the 20mm and 40mm procurement programs.[6] Until the spring of 1940 the Naval Gun factory, Washington, D. C., was the only manufacturer of 1.1"1 guns and mounts. At that time a production rate of 36 a year was reached, but in the light of the needs of a rapidly expanding fleet this figure was obviously inadequate. To meet the increasing demands, commercial plants were surveyed with the



idea of placing contracts for the manufacture of a parts, final assembly to be made at the gun factory.[7]

In the meantime President Roosevelt, in May 1940, suggested that in order to speed production the Navy should construct and equip a plant for the manufacture of 1.1" guns under a private management contract. The Bureau, however, was of the opinion that the quickest, most economical, and moat efficient way to obtain these urgently needed guns was to exhaust the potential capacity of private firms. It was believed that by making use of some of the commandeered foreign machine tools, selected companies could be speedily equipped to go Into immediate production not only of the l.l" but of the 5" AA gun as well. It was also pointed out that the plan utilized firms already well organized and with an adequate labor market at hand.[8] The




President approved with the admonition "Speed it ..."[9]

The Bureau, as a result of its previous survey of potential producers, was able to place contracts for Increased l.l" production in a very short time. Under the accelerated program the Westinghouse Electric Manufacturing Company became the contractor for complete mounts, the Packard Motor Company produced the three major parts of the breech assembly as well as some of the smaller parts, the Nash Motor Company supplied the ammunition cradles, and the Bridgeport Thermostat Company manufactured the magazines. Other contractors added during the summer and fall of 1940 included the Graham-Paige Corporation which produced firing pins, breech housings and cartridge guide plates; the Budd Manufacturing Company, mechanisms and cradles; Sipp-Eastwood Corporation, plungers and retracting tools;




Wlllys-Overland, breech housings and recoil cylinders; the New Products Corporation, Aldon Products Company; New York Air Brake Company; Orange Roller
Bearing Company; Rollway Bearing Company, and the Standard Machinery Company.[10] In addition the Naval Gun Factory, contracts for gun barrel forgings were placed with the Midvale Company, the Crucible Steel Company, and the Pennsylvania Forge Company.

Soon after this speed-up was initiated the Bofors gun was introduced to replace the l.1". Its adoption, of course, decreased the total number of 1.1" guns originally estimated as necessary, and on a thorough review of the situation it was determined that a total of 823 assemblies would be sufficient to meet all Bureau requirements.[11] The manufacturers encountered no major difficulties In meeting this requirement, and as contracts were



completed, production facilities were channeled, if at all possible, to the rapidly expanding 40mm program. [12]

The Naval Gun Factory assembled all l.l" guns from parts manufactured by the various contractors. Following assembly the guns were proved at the Naval Proving Ground, Dahlgren, and returned to the Gun Factory for overhaul and shipment* Only one mount In twenty was proved at Dahlgren; the others going directly from the manufacturer to installation and storage points.[13]

2. Power Drives

The failure of power drives to keep pace with the output of gun and mount assemblies constituted the major bottleneck in the 1.1" production program.
The first production contract for power equipment for the 1.1" was placed with Vickers Incorporated



early In 1935. It called for the delivery of 33 electric-hydraulic power drives which were to be operable in local or manual control. Production was halted when It was found that the slewing arrangement permitted training at too high a speed for the safety of operating personnel.[14]

Development of l.l" drives capable of operating In manual, local and automatic control was not Initiated until September 1940 at which time a Letter of Intent was Issued to Ford Instrument Company for the development and delivery of drives. Production was scheduled for 350 unite at a rate of 20 drives a month. However, In March 1941 this quantity was increased to 900 and production capacity authorized for 40 unite a month. This drive, of the electro-mechanical type, after use by the Fleet proved to be unreliable and faulty In basic design. Frequent breakdowns were common due to the



overheating of the magnetic clutch-type transmission and the failure of the limit stops.[15]

The General Electric Company, originally operating under a letter of intent of June 21, 1941, developed an amplidyne-type drive, the Mark 3, which proved reliable. The drive was superior to the Ford product and was well received by the Fleet, it was replaced by the G.E. drive, Mark 4, which could be used on both the l.l" and 40mm twin gun mounts.[16]

The production of l.l" drives totaled 552 of which 206 were produced by Ford, 279 by General Electric, and In the closing days of the program, the NOP Center Line was brought in to assemble 67 of the Mark 4 drives. The last of these drives was not delivered until 1944.[17]

The delay in power drive production is well illustrated by comparing the monthly cumulative gun




and mounts assembly with the rate of conversion from hand driven to power driven mounts:


Gun & Mount

Power Drives
July 1, 1940 to
December 31, 1942


May 1, 1942


June 1, 1942


July 1, 1942


August 1, 1942


September 1, 1942


October 1, 1942


November 1, 1942


December 1, 1942




It is a significant fact that the drives developed for the 1.1" were adapted or modified for the 40mm in order to hasten the installation of this equipment in the Fleet during the early stages of the war.[18]



c. Distribution and Disposition

Practically the entire production of the 1.1" program was devoted to United States Navy use. Only 4 of the 823 assemblies were installed on merchant vessels and less than 1% were exported under Lend-Lease.[19] Installations on Navy combatant ships totaled:[20]



Total Number38168155134970
Percentage by Type      
CV, CVL, CVE3200000
CA, CB020000


1.1" Installations on Navy Combatant and Other Ships
InstallationsCombatantOther (Including
Coast Guard
June 30, 194439439%61%
December 31, 194440633%67%
June 30, 194525143%57%



Over 200 assemblies were channeled to the shore defenses of various Naval Operating Bases, to Navy training activities, and to special Army vessels. In addition to the installations afloat and at shore stations 130 spares were procured and maintained for service replacement.[21]

The following tabulation summarizes the procurement and disposition of 1.1" quad mounts Mark 1 and Mark 2:[22]

1.1" Mounts Mark 11.1" Mounts Mark 1
Disposition as of
30 June 1945
 Disposition as of
30 June 1945
To be scrapped 47Defense Aid5



Shortly after the surrender of Japan the Board and Working Committee for the Determination of Obsolete and Excess Ordnance Equipment made the following
recommendations for the disposition of 1.1" equipment:[23]

(1) Retain 190 power drives Mark 4 for use with 40mm twins.
(2) Declare obsolete all mounts and gun mechanisms in store and dispose of all In excess of spares requirements for mounts afloat as scrap.
(3) Declare obsolete all mounts and gun mechanisms upon removal from ships and discard as scrap.

These recommendations were approved by the Chief of Naval Operations.



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Transcribed and formatted by Thomas Wildenberg, HyperWar Foundation