20mm Antiaircraft Gun

Chapter V

a. Introduction

In 1935 the Bureau of Ordnance purchased two heavy 20mm machine guns from the Oerlikon Machine Tool Works of Zurich-0erlikon, Switzerland, for test as aircraft and antiaircraft weapons. The guns were delivered to the Supply Officer at the Navy Yard, New York, on September 12, 1935, and comprised the following material:

1 Aircraft Gun Type FFL

1 Swivel Ring FRL

1 Aircraft Gun Type L

1000 Cartridges HL Type FF
1000 Cartridges HL Type L

These guns, 1934 models, were low velocity weapons with a rate of fire of only 265 rounds per minute. Following thorough tests at Dahlgren and the Aberdeen Proving Ground the guns were rejected. The Bureau was of the opinion, that the development of the caliber .50 machine gun offered a superior antiaircraft weapon; while the Army was equally certain that the Hispano-Suiza possessed



superior advantages as an aircraft cannon. The Japanese adopted the 1934 model, which at the time of Pearl Harbor was their standard aircraft and antiaircraft gun. It is interesting to note that the licensing agreement concluded with Japan saved the Swiss Oerlikon Works from bankruptcy and made possible the improvement of the 20mm gun as an antiaircraft weapon--a weapon which was used eventually so successfully by the United States and Great Britain against the Japanese.[1]

The high hopes of the Bureau for the caliber .50 antiaircraft machine gun did not materialize, and by 1940 it was realized that a gun of larger caliber was necessary to meet the menace of dive bombing. The Oerlikon 20mm antiaircraft gun, a much superior weapon to the 1934 model, was chosen to replace the lighter gun. This adoption was so intimately connected with British experience that


understanding of the Bureau's action.

b. Background of Adoption of the 20mm [2]

1. Early British Activities

In 1937 the Royal Navy Initiated tests to find a suitable weapon for the defense of merchant ships, trawlers, mine sweepers, and similar vessels, against dive bombers and close range air attack. One of the principal requirements for the gun was that it could be operated by non-specialist personnel, such as merchant seamen and fishermen. As a result of these tests, the Navy selected the 20mm antiaircraft gun which was manufactured by the Oerlikon Machine Tool Works of Zurich--Oerlikon, Switzerland.
A contract was negotiated with the Oerlikon Company for the manufacture and supply of these guns.



In addition a license agreement provided that the Oerlikon Company would supply the Admiralty complete information to enable them to produce by themselves, or to their order in any part of the British Empire, the Oerlikon type SS/SLA equipments, and also the ammunition types SG, HL, UG, and UL, including rotor fuzes.

In June 1940, shortly before the fall of France, and as the war situation was growing steadily worse for neutral countries in Europe, the British decided that it would be advisable to establish a source for the manufacture of these guns in the United States. Shortly before this, on March 1, 1959, the Oerlikon Company had appointed Mr. Alfred Altman of New York as their representative in the United States. The agreement between Oerlikon and Altman provided for a commission of 5% for guns, mounts, and ammunition, and 10% on all license transactions. The license transaction was limited for use in and for the United States. Further, the extension of the license agreement



beyond December 31, 1940, was contingent upon Mr. Altman's concluding "transactions amounting to at least 500,000 United States dollars."

In the meantime, Mr. Antoine Gazda, who styled himself "Export Manager, Oerlikon Works," arrived in the United States late in May of 1940. Gazda, in preliminary negotiations with the British, promised that he would be able to produce Oerlikon guns at an annual rate of 2000 five months after receipt of a firm order, estimating that it would require three months to complete tooling and two months lead time before the delivery of the first gun. On August 9, 1940, in a conference with officials of the British Purchasing Commission, Gazda stated that he intended to Incorporate a company in the United. States as an assembly plant, and use subcontractors for the manufacture of guns, mounts and ammunition.

There was no close liaison between the Oerlikon representatives, Altman and Gazda. In fact, Gazda stated that Mr. Altman's contract was the primary



reason that he did not make a serious effort to sell the gun to the United States as he did not want to pay Altman 5% of the sales. However, Gazda held a power of attorney from the Oerlikon Machine Tool Company, dated December 30, 1940, which authorized him to negotiate a license agreement for the manufacture in and for the United States of America and export to the United Kingdom of the Oerlikon guns type SLaSS and ammunition types HL, SG, UL, and UG. The agreement was subject to the consent of the Swiss Government.

Mr. Gazda was successful in interesting Mr. Carl H. Behr of the New York banking house of Dillon, Read and Company, in organizing an American Corporation to manufacture the Oerlikon gun. On October 16, 1940, the Corporation was chartered by the State of Delaware under the name of The American Oerlikon Gazda Corporation. Mr. George A. Rentschler was Chairman of the Board and Mr. George H. Houston, formerly President of the Baldwin Locomotive Company, was President. The company was



75% American owned, Mr. Gazda holding only 225 shares of preferred stock and 2500 common.[3]

2. Adoption of the Gun

On September 23, 1940, Mr. Philip Young, a member of the President's Liaison Committee, advised the British Purchasing Commission that approval P.N.R.A. 17, which was issued on September 21, 1940, subject to no interference with Navy Commitments, was withdrawn in accordance with the policy that no clearance would be given for complete guns which were not standard to those used by the armed forces of the United States.

At this point the British began a serious campaign to have the United States adopt the 20mm Oerlikon gun. On October 31, 1940, the Admiralty cabled Arthur B. Purvis of the British Purchasing Commission:

The Admiralty are greatly concerned to learn through telegram ADCAN 360 from their Mission that the United States Government has withdrawn permission to manufacture Oerlikon gun equipments and



that this may be withheld altogether unless the United States Navy decides to accept this weapon.

The Admiralty would regard such a decision, if final, as a staggering blow to their preparation for antiaircraft arming of small ships and mosquito craft. The selection of the Oerlikon was the result of exhaustive test and experience under war conditions, and on the cessation in May last of supplies just begun from Switzerland they turned to the project for Oerlikon production in the United States of America as the only means of satisfying their vital needs. In June last, they Informed the British Supply Board that requirements existed for 2000 guns and mountings and 10,000,000 rounds. Loss of time would be irreparable if it is now rendered nugatory. Request you will make every endeavor before leaving to contact Morgenthau and the Secretary of the Navy and earnestly urge immediate consideration of permission for Oerlikon production. To the Navy Department we suggest that you say that the explanation given by Comdr. Mitchell of reasons for rejecting the Hispano-Suiza be given full weight. They are based on the experience of poor functioning in small ships where the high standard of maintenance called for is impossible.

On November 8, 1940, Mr. Purvis addressed Colonel Frank- Knox, then Secretary of the Navy, urging him to adopt the Oerlikon as a standard Navy weapon.



In the meantime Captain W.H.P. Blandy, Antiaircraft Type Assistant, had already reached the conclusion that the Oerlikon was the best gun for naval use and had recommended its adoption to Admiral Furlong, then Chief of the Bureau. Following Mr. Purvis's letter to the Secretary, Captain Blandy wrote a memorandum to the Aid to the Secretary advising that he had arranged firing tests at the Naval Proving Ground the preceding week and all officers present were favorably impressed with the performance of the gun. He further informed the Aid that Admiral Furlong had approved his recommendation that morning, November 9.

3. Reasons for Selection of Oerlikon over the Hispano-Suiza.

At the time of the adoption of the Oerlikon the Navy already had a powerful 20mm machine gun in the Hispano-Suiza used in both Navy and Army aircraft. This gun had a much higher rate of fire than the new Oerlikon and it offered the further



advantage of a common gun and ammunition for both services. Because of the general undesirability of having a second 20mm gun manufactured In the country, the Army was reluctant to see the Navy adopt the Oerlikon for antiaircraft use. The Bureau had considered this phase of the situation, but In view of the severe limitations of the Hispano-Suiza as an antiaircraft weapon, It had very little choice in the matter.[4]

The Oerlikon offered greater reliability because of the greater reserve of power. It was operated by maximum gas pressure, about 23 tons per square Inch, and by springs which were correspondingly powerful. On the other hand the Hispano-Suiza was operated by reduced gas pressure of about 8 tone per square inch and by springs similarly week. It was apparent that the forces at work in



the Oerlikon were consequently greater than those in the Hispano, and hence such factors as friction, the effect of different elevations, cold weather, rain and the like, were too small in proportion to the operating forces to cause stoppages. Primarily as a result of this reserve power, the Oerlikon did not require skilled service maintenance.

One of the greatest advantages of the Oerlikon over the Hispano was the fact that it had a barrel which could be replaced in about 30 seconds. Since an airplane gun fired very short bursts, and was mounted In the wings of a plane moving through the air at a high rate of speed, it did not present much of a cooling problem. The Hispano was therefore designed without any thought of permitting a change of barrels during action; in fact, it was hardly possible under such conditions. At sea, however, against multi-plane dive bombing attacks,



prolonged firing was necessary and the ability to change barrels quickly was of great importance.

The magazine employed with the Oerlikon was superior to the Hispano's. In this first place the Oerlikon magazine could be kept fully loaded without any tension on the springs while in the Hispano the spring was compressed as long as the magazine was loaded, a condition which brought about occasional spring collapse. Secondly, the magazine had a greater reserve because of the easier task of feeding at 490 r.p.m. as against the higher rate of the Hispano's 620. Thirdly, the Oerlikon magazine had a straight tangential lead through its mouthpiece, whereas the Hispano had a 90° bend.

Another deciding factor in the adoption or the Oerlikon was the fact that it had a simple mount for antiaircraft use, while a mount for the Hispano had not at that time been designed.


The sea experience of the British with the Hispano-Suiza proved the superiority of the Oerlikon. After the fall of France supplies of Oerlikons from Switzerland were cut off, and as a stop gap Hispano guns were Installed on several escort vessels. The results were uniformly bad. Snips reported frequent stoppages from the unsatisfactory design of the cradle, salt water corrosion around the breech block, unlocked tappets, and the collapse of the magazine springs. It was also found that when water got into a hot gun barrel stoppage was likely to occur on the reopening of fire due to steam in the gas port. The guns were so unreliable that one vessel reported that she preferred not to open fire with the Hispanos in the hope that the Germans would think she was not a warship. Opposed to this, the British experience with the 100 Oerlikon guns at sea in November of 1940 was uniformly excellent.

c. Production Program

1. Preliminary Contract "Negotiations

Shortly after the adoption of the Oerlikon



gun, the Bureau called a conference with the B.P.C. for November 20, 1940, to work out a joint program for the purchase of 20mm guns. The total quantity of guns under consideration was 5,000, of which the British were to receive 4,000 and the United States 1,000, It was also decided that there should be at least two sources of supply in this Joint effort. The British thought a reasonable condensation to the Swiss Oerlikon Company and Gazda should be:

On the next 2,000 guns, $300 600,000
On the third 2,000 guns, $100 200,000
On the first 2,000 guns, $600$1,200,000
On the next 2,000 guns, $300600,000
On the third 2,000 guns, $100200,000

Royalties were to cease after this gun had been paid. Bureau officials considered $1,000,000 ample.[5]

At this meeting Commander Mitchell agreed to forward to the Bureau six sets of complete specifications, tool and manufacturing drawings. The drawings were received on November 25, 1940, and


were sent immediately to the Gun Factory to obtain recommendations for manufacture and approximate estimates of costs upon which to base negotiations.

Meanwhile, the British were negotiating with Gazda for a license and for Swiss technicians to aid in setting up production in this country. Gazda proposed a fee of $838,000 for the license and 3% of sales. The British considered the demand exorbitant, and after lengthy conference a proposed contract NOA-3594, dated March 8, 1941, was negotiated between the B.P.C. and the Oerlikon Machine Tool Works. The proposed agreement provided for an adequate technical staff of at least five Swiss experts approved by the British Government, and for the payment of licenses, drawings, and services as follows:

On the first 2,000 equipments          $300 each 
For the second 2,000 equipments    $200 each
For the next 6,000 equipments        $100 each

After these payments no further fees were required for a period of five years after the date of the execution of the contract.



In effect this proposal constituted the granting of a license for five years for $1,600,000. The agreement, however, was subject to the approval of the Swiss Government which had prohibited, on August 30, 1940, the granting of rights of any kind relating to the use of inventions, whether patented or not, secret processes and industrial experience concerning the manufacture of war material. The agreement provided that the Oerlikon Company would obtain the consent of the Swiss Government for the license. The British soon canceled the proposed contract following a delay in getting approval.

The failure to receive the consent of the Swiss Government did act deter the British, and the American Oerlikon Gazda Corporation continued to operate under a letter of intent for the production of 2000 guns.[6] A formal contract was never executed between the British and the American Oerlikon Gazda Corporation. A proposed cost plus fixed fee contract,



dated June 23, 1941, was drawn up which called for the production of 2000 guns, 16,000 magazines and the necessary spare parts. The British, however, had in mind turning the proposed contract over to the United States under the Lend-Lease Act. This was done, and on August 9, 1941, the Bureau negotiated Contract NOs-90588 with the American Oerlikon Gazda Corporation. The contract provided for the production of 2500 complete assemblies, 2000 of which were to go to the British. Deliveries were to begin in August with fifty equipments and were to attain a maximum rate of 200 per month by October 1941.[7] In this connection it is interesting to note that the first gun produced by the American Oerlikon Gazda Corporation and its subcontractors was fired successfully on June 8, 1941--two months before the execution of the formal contract.

The contract of August 9 was subject to Section 11 of the Act approved June 28, 1940 (Public



671, 76th Congress) which provided that no aliens be permitted to have access to the plans or specifications of work under secret, confidential or restricted government contracts. Gazda therefore had to be placed by the American Oerlikon Gazda Corporation as a director. This was not regretted by the Bureau as it was suspicious of Gazda because of his international arms dealings and because of his many extravagant claims and allegations concerning his part in producing the gun. After the elimination of Gazda the name of the company was changed to the A.O.G. Corporation.

During the negotiations between the British and the American Oerlikon Gazda Corporation, the Bureau, in accordance with the decisions reached at the November 20 conference, was attempting to secure another source of supply. After much effort the Pontiac Motors division, of the General Motors Corporation was interested In the program, and on.




April 3, 1941, the formal contract was negotiated. The contract called for 2000 equipments for delivery to the British under Lend-Lease. Deliveries were scheduled to begin thirty days after the completion of the installation of facilities--a rather indefinite date. However, before production was initiated an option for the production of 4000 additional equipments was taken up, and deliveries were advanced to 400 a month.

On May 22, 1941, the Hudson Motor Car Company was brought into the program. Deliveries were scheduled at a rate of 200 a month. The Hudson Company was also given a contract for the preparation of drawings, pamphlets and design work. It was at the Jefferson Avenue Plant of the Hudson Company that the Swiss drawings were converted to American production standards. It is interesting to note that the original mechanism continued in use without major change and with complete inter-changeability of parts until the end of the war.



The Pontiac Motor Division completed its first equipment In September 1941, but it was not until after Pearl Harbor that Hudson was able to make delivery of a 20mm gun and mount. Deliveries during the prewar months were disappointing. Of course, the three prime contractors were setting up facilities, taking deliveries on tooling, revising drawings, and adapting the Swiss watch-like mechanism design to American mass production. At the time of the Japanese attack on Pearl Harbor only 379 equipments had been delivered. Of this total the AOG had produced 264 equipments to Pontiac's 115.[8]

2. Increasing Requirements

By early December 1941, the preliminaries to mass production had been disposed of to a degree that permitted the impetus afforded by actual war to be reflected immediately in a rapid acceleration of production. Actual deliveries for December were nearly 30%, and for January over 80%, greater than



earlier expectations.[9] At this time production rates for the three prime contractors had been authorized to provide a total monthly delivery of 1,850 complete equipments. Of this total the NOP, Center Line, was to produce 750, Pontiac 600, and the A.O.G. Corporation 500.

The demands of the U.S. Navy and the prospective requirements of the US Merchant Marine for 20mm antiaircraft guns, plus the pyramiding requisitions for Lend-Lease forced the Bureau, early in 1942, to increase the rates to 3,250. Monthly deliveries were scheduled as follows:[10]

Pontiac                           1,250
NOP, Center Line          1,250
A.O.G. Corporation         750

Before the higher rates were authorized it was necessary for the Bureau to provide the prime contractors with additional facilities since it was no longer possible for them to absorb the total increase by additional subcontracting. It is significant that



by April 1942 the production of 20mm guns had been in sufficient numbers to permit the arming of new construction and ships of the existing Fleet, as well as permitted the original installation of the weapon on auxiliaries and merchant ships.[11]

The next major change was negotiated in the summer of 1942 and Involved an increase in the monthly mechanism production from 3,250 to 3,900. Following this expansion the productive rates of the three prime contractors were:

Pontiac                        1,450
NOP( Center Line       1,450
A.O.G. Corporation    1,000

The excess production of gun mechanisms over mounts was necessary to meet requirements for issues of spares to the Fleet, and to provide mechanisms for two new mounts coming into production at the Continental Gin Company (Mount Mark 10) and the Cameron Iron Works (Mount Mark 6). The Cameron Iron Works had been authorized to produce 300 mounts



a month and the Continental Gin Company was scheduled at 400.[12]

In early 1943 the heavy demands of the landing craft program brought a further acceleration in 20mm mount procurement. Maximum production was set at 4,560 and monthly allocations distributed as follows:

Pontiac                                  1,500
NOP, Center Line                 1,500
A.O.G. Corporation                 850
Continental Gin Company         400
Cameron Iron Works               300

At the same time mechanism production was raised to 5,350. Under this new schedule monthly deliveries of the prime contractors totaled;[13]

Pontiac                                 2,050
NOP, Center Line                2,050
A.O.G, Corporation             1,250

The surplus production of mechanisms over mounts was to provide spares for both Fleet and maintenance activities and to meet Lend-Lease requirements.



The 20mm program attained its peak in September 1943. During this month mechanism production reached an all time high of 5,630 and the mount production, likewise an all time high, totaled 4,693.[14]

3. Mounts

Single Mounts

Many new designs of different types of mounts were submitted to the Bureau for consideration during 1941 and 1942. The Mark 4, then currently in production, was a very heavy mount which weighed approximately 1,300 pounds. It also utilized expensive gears and bearings. The mount was not watertight and was very poorly lubricated. Although lit was designed to permit an operator to raise and dower the trunnions to accommodate the gunner, after operating at sea for short periods this feature often became inoperative due to rust and corrosion. Over-was quite expensive and necessitated replacement



of parts difficult to manufacture.[15]

The Mark 4, In spite of Its limitations, generally performed satisfactorily in service. There were, however, special uses for which a simpler and lighter mount was desirable. To meet this need a new mount, the Mark 10, was designed by the Naval Ordnance Plant, Center Line. The Mark 10 weighed 725 pounds less than the Mark 4, and an additional saving of 250 pounds was affected by omitting the shield and shield brackets. Lightness was purchased at the cost of adjustability of trunnion height, though it was soon proved that in most cases the reduced weight more than compensated for the advantages sacrificed. The trunnion height was fixed at approximately 52" in order to provide the best general accommodation to gunners of various heights. An additional advantage of the mount was that it permitted gun depression to 15°. It should be pointed out that when the Mark 10 was designed it



was not intended as a replacement for the Mark 4 on the larger combatant ships, but was meant for the smaller types of vessels In which the weight saving feature was specially important, as well as for merchant vessels where it was desirable to eliminate the extra crew member who would otherwise be needed to adjust trunnion height.[16]

The Continental Gin Company of Birmingham, Alabama, delivered the first Mark 10 in January 1943, The first mounts were not completely satisfactory as there was high torque in training and excessive vibration. There was also doubt whether it could be used with the Mark 14 sight. However, these difficulties were eliminated and the mount was authorized for standard installation, either with or without the Mark 14 sight. The way was then clear to cancel production of the mount Mark 4. It is interesting to note that at the time this change was made the


--70 --

Mark 4 cost as high as $1,800.00 at the Textile Machinery Company, a subcontractor, and that the cost of the Mark 10 was below $500.00.[17]

A total of 60,521 mounts Mark 4 were produced by the three prime contractors--Pontiac, A.O.G. Corporation, and the NOP, Center Line. The bulk of this procurement was completed before the Mount Mark 10 attained full scale production. The Mark 10 program Involved the procurement of 43,791 mounts from Pontiac, Center Line, A.O.G., Continental Gin Company, and the Modern Welding Company.

A development which paralleled the Mark 10 was the hydraulic mount Mark 6 which was designed by the Pontiac Motor Division of General Motors. The adjustable trunnion height feature of the mount was operated by foot pedals which controlled a hydraulic system which raised and lowered the trunnions. The first contracts for this mount were



placed with the Cameron Iron Works of Houston, Texas, In peacetime a manufacturer of gasoline pumps and oil equipment. The rate of production originally authorized at 200 a month was later increased to 300. In the spring of 1943 Pontiac was authorized to deliver half its production in mounts Mark 6 and soon afterwards NOP, Center Line went into production at a rate of 100 a month.

Although a total of 10,312 Mark 6 mounts were procured, their performance was never satisfactory. Very few of these mounts passed a satisfactory proof at the Naval Proving Ground. The primary trouble was excessive vibration and the rising of the hydraulic ram during firing, the cause of which could not be remedied. The mount was also hard to maintain. It was eventually replaced by the Mark 10.[18]

Another Interesting mount was the Mark 5, known as the fixed-height pedestal type. The design was



of British origin, and although slightly modified by the Bureau, the mount remained essentially the same. The fixed trunnion height feature eliminated the expensive gears and bearings required in the mount Mark 4, thus reducing the cost. There was no great saving in weight since it was necessary to build steps or platforms for the gunners. Procurement of these mounts ceased after the mount Mark 10 went into full scale production. A total of 6,101 mounts Mark 5 were produced, the British receiving all but
916 of this number.[19]

In 1942 there was a requirement for a portable platform for the use of 20mm AA guns and mounts Mark 10 in landing operations, and the United Shoe Machinery Company of Beverly, Massachusetts, was commissioned to perfect a design. The design was completed early in 1943, and a contract was placed with the Continental Gin Company, Birmingham, for



the production of 3,000. Subsequent contracts brought the total to 4,500. In April 1944 the program was cut back to the original 3,000. Though the platform was designed primarily for use with the 20mm gun mount Mark 10, it was also usable with mounts Mark 4, 5, and 6.[20] It was reported, that this equipment had very little service use.

Twin Mounts

The 20mm twin mount was developed by the Bureau to increase the close range antiaircraft fire power of Navy ships. Initiated early in 1944, the mount was completed and successfully tested by September 1944.[21]

The new mount, designated the Mark T-4, consisted of two gun mechanisms set parallel positions 6 1/2" apart on what was essentially a Mark 10 Mod 23 mount. A new and improved



cam limit stop was Incorporated as a component part of the mount. In addition to handle bars and shoulder rests, ball bearings were provided to decrease the training effort to a minimum. Working circle requirements of the twin and single assemblies were essentially the same as were the angles of elevation and depression.[22]

The weight of the mount Mark 24 when equipped with shields and gunsight Mark 14 was approximately 1400 pounds, as compared with 1900 pounds for the similarly equipped mounts Mark 2 or Mark 4, and 1000 pounds for the Mark 10 assembly. The weight of the twin assembly minus the shield and gunsight approximated 1000 pounds as compared with 750 pounds for the Mark 10.

In comparison with the single assembly the twin mount had the greater fire power, required fewer men per barrel for its operation, either barrel fired singly at all angles without undue slewing,



and there was practically no increase in space or silhouette. On the other hand the right and left magazines were not interchangeable thus requiring additional stowage; and in order to clear a jam in one barrel, both barrels had to cease firing.[23]

The Bureau recommended, and CNO approved, the installation of the twin assembly where practicable in combatant ships, landing craft and auxiliaries, to replace 20mm singles on a weight for weight basis.[24] Under this policy twin assemblies replaced singles in the ratio of three twins to four single Mark 2 or Mark 4 assemblies (a gain of 2 barrels with a savings of 4 men), or in the ratio of three twins to five single Mark 10 assemblies (a gain of 1 barrel and a savings of 2 men.) The production of these mounts was centered in the NOP, Center Line as the prime contractor. The


first mount was delivered in February 1944, and at the end of the program in December 1945, a total of 8,300 mounts had been produced.

4. Cutbacks and Terminations

In the fall of 1945 the production of 20mm guns and mounts was sufficient to meet all requirements. The increasing popularity of the 40mm with the Fleet as the best weapon for close-in antiaircraft defense plus a curtailment of the shipbuilding and landing craft programs made inevitable a cut in 20mm procurement. The Bureau decided to meet this situation by making a horizontal reduction of approximately one-third at each of the prime contractors - Pontiac, NOP Center Line, and the A.O.G. Corporation. Some thought was given to eliminating the A.O.G. Corporation as it was the high cost producer, but the general opinion was that since the war was still in progress with future requirements uncertain, it would be foolish to relinquish the entire productive capacity of any one of the prime contractors.[25]



However, it was stated that in case of future reductions, price, next to deliveries would be a paramount consideration. Production at the Cameron Iron Works was terminated as the mount Mark 10 was rapidly supplanting the heavier mount Mark 6. Contracts at the Continental Gin Company were allowed to run out.[26]

In March 1944, following a. revision of CNO's requirements from 11,000 to 3,000, the Bureau handed the A.O.G. Corporation a notice of the termination of the prime contract. The Corporation, in keeping with the terms of the contract, was given ninety days notice of the effective date of termination.[27] The principal lesson learned from this experience was that the terminations should be conducted in such a manner as to allow the subcontractors to complete all work in process rather than leave semi-finished parts in the termination inventory.[28]



By the fall of 1944 further cute in the 20mm program were indicated. This time a choice had to be made between Pontiac and the NOP, Center Line. In view of the existence of Government-owned facilities which were regarded as adequate for future requirements, and in keeping with the declared policy of building up the NOP's, the Bureau determined that it would not be feasible to retain Pontiac as a prime contractor.[29] A ninety day no-cost termination plan was agreed upon, and the termination of this contract cost the Government no money.

A few weeks after Pontiac's contract was terminated, 20mm requirements dwindled to the point where no further production of single mounts was required at the NOP, Center Line. Here again agreements were effected for low cost termination. The actual producer was Borg-Warner Corporation, a subcontractor. It was possible to divert some of the material from



the termination of the single mount Mark 10 to the production of the new 20mm twin mount Mark 24 which was to be produced at both Center Line and the Borg-Warner Corporation. Borg-Warner Corporation was given an order to produce 4,000 of the twin mounts and Center Line was to produce 1,000. A schedule was set up to transfer the facilities from Borg-Warner at the end of production, approximately June 1945, to Center Line where production would continue.[30]

In June 1945 requirements for the 20mm twin Mark 24 skyrocketed to over 25,000, and the Bureau placed orders for 21,000. After V-J Day, this program like all others was cut substantially and production stabilized at 6,321 complete equipments. Delivery was completed in December 1945, thus bringing to a close the 20mm program - the largest single program in the Bureau.[31]



5. Costs

The procurement of 20mm single and twin assemblies involved and expenditure of approximately 1500,000,000. Over 55450,000,000 of this total was absorbed in the purchase of 125,735 single assemblies, the largest Bureau expenditure in any gun and mount program.[32]

The 20mm program was characterized by a gradual reduction in costs. As was to be expected with any new weapon, the original costs were high, but as the three prime, contractors perfected their organization and effected improvements in production techniques, the prices were reduced to such an extent that at the end of production they approximated, on the whole, roughly 50% of the original costs.

Under the first contracts with Hudson (NOP, Center Line) and Pontiac, the 20mm gun and mount



Mark 4 cost, excluding the 7% fee, approximately $7,000. The unit cost at the A.O.G. Corporation was estimated at $6,500 plus a fee of $266.00 for each equipment.[33] The position of A.O.G. as the low cost producer was due in the main to the fact that it had been in production for several months on British 20mm contracts at the time the United States took over. This distinction, however, was soon lost when Pontiac and the NCP got into full scale production. It is interesting to note that in 1940 during the British negotiations with A.O.G. Corporation the estimated cost was $12,000 for the mechanism and $3,000 for the mount.[34]

The decreasing cost of 20mm equipment is excellently Illustrated by the price history of the Pontiac contract.[35]



  Gun & Mark IV MountGun & Mark X Mount
 Effective PeriodNo. of UnitsUnit PriceNo. of UnitsUnit Price
Cost Plus Fixed Fee  $ 7,490  
1st Fixed PriceSep. 1941 through Dec. 194212,7695,136  
1st ReductionJan. 1, 1943 through Feb. 28, 19432,8004,642  
2nd ReductionMar. 1, 1943 through Mar. 31, 19431,3994,238None$ 3,614
3rd ReductionApr. 1, 1943 through Jun. 30, 19433,1323,9681943,263
4th ReductionJul. 1, 1943 through Oct. 31, 1943  2,6792,990
5th ReductionNov. 1, 1943 through Dec. 10, 1943  1,1372,369
6th ReductionDec. 10, 1943 through Dec. 31, 1943  1152,342
7th ReductionJan. 1, 1944 through Mar. 31, 1943  2,9112,177
8th ReductionApr. 1, 1944 through Jun. 8, 1944  3,8231,783
9th ReductionJun 9, 1944 through Jul. 31, 1944  3,8231,783
10th ReductionAug. 1, 1944 through Nov. 31, 1944  11,1021,658
  ======= ====== 
TOTAL UNITS 20,100 23,790 



The detailed price history of the 20mm contract with NOP, Center Line was not available, but It Is known that there was very little difference in costs at Pontiac and Center Line. Another interesting sidelight was that production costs at the A.0.G. Corporation were lower than at Pontiac or Center Line when rates were less than 700 equipments per month. However, when production increased to over 700, A.O.G. became the high cost producer.[36]

6 .Speeding Production


In meeting the increasing requirements for 20mm equipment the prime contractors made extensive use of subcontractors, and at the same time Increased the efficiency of their own production. It was the firm policy of the Bureau to require prime contractors to subcontract as much as practicable, having due regard for prompt delivery of



satisfactory material, in order to reduce costs and conserve raw material incident to new plant expansion, to alleviate bottlenecks on machine tools, and to effect earlier deliveries.

The 20mm program furnished an excellent illustration of this policy. As pointed out previously, the A.O.G. Corporation was an assembly plant only, 100% of its work being subcontracted, Pontiac subcontracted 175 out of the 195 parts for the weapon, but elected to manufacture the 20 most difficult pieces. These included the gun barrel and breech mechanism, which accounted for 45% of the value of the gun because of the large number of tedious operations which had to be performed on nearly every piece. The breech casing, an extreme example of complexity, required some 250 operations. In all, Pontiac utilized 94 subcontractors.[37] The NOP, Center Line, subcontracted approximately 60 to 65%


of the gun and mount order.[38] It had 17 prime subcontractor; each of which had six or more subcontractors in turn supplied by contributing producers on down to the steel mill and fabricator. In addition to the chair of production there were 126 companies which supplied finished manufactured parts.[39]

The three prime contractors encountered considerable difficulty in locating subcontractors in the period preceding Pearl Harbor. However, in this respect 20mm procurement was not unique; similar difficulties characterized most of the Bureau's important production programs during this time. Manufacturers were busy with the biggest and most profitable peacetime business in years, and many were unwilling to swap this sure profit for the nebulous advantages offered by a defense contract


for the production of new and complicated war material.

In the early days of 20mm procurement the close tolerances made necessary considerable tooling, and coupled with the small quantities Initially required did much to steer potential subcontractors away from the program. Then too, all drawings carried Navy Department material specifications; specifications with which civilian firms were not fully acquainted. Further, most of the parts required-steel of special sizes and analyses which was not available in warehouses, and the mills, extremely busy, were not interested in making short runs even though contractors were willing to take minimum procurable quantities. In spite of these drawbacks, and with much effort on the part of prime contractors, satisfactory subcontractors were located. Perhaps the greatest trouble was experienced in locating subcontractors for miscellaneous machine gun parts. On these pieces it was necessary, in a


great many cases, to resort to Jobbing machine shops as well as tool sources, and often limited quantities had to be made by tool room methods at prices much higher than normally expected.[40]

As the program progressed under wartime impetus, relief was given to a great extent by modification of tolerances, and in some cases by simplification in design. Also, guns and mounts were authorized in increased quantities which enabled the prime contractors to offer greater volume of production to subcontractors thus bringing in new sources of supply.

The prime contractors endeavored to subcontract entire assemblies. In many instances the magazine mount, shoulder rest and sight were all subcontracted as entire assemblies. The more or less standard or near standard items, such as springs, were procured



by purchase order. Accessories--pliers, wrenches, spanners--were also purchased items. Purchase orders for the procurement of the more standardized articles were placed with manufacturers whose products were closely allied to the items required by the prime contractors. In general, where the prime contractors could relieve themselves of added administrative responsibilities by depending on the "know-how" and experience of the manufacturer, they did so.

Attention was also given to the size and capacity of the plant of the prospective subcontractor. The prime contractors desired that the subcontractor be in a position to accept the order and still have the capacity and flexibility to absorb increases both in quantity and delivery rates occasioned by an accelerated production program. If the manufacturer was able to accept only a limited contract due to other obligations or an otherwise limited


capacity, It was thought best to look elsewhere for in case of increased demands other sources would have to be opened, resulting in additional negotiations for a contract and delays in expanding the program.

Some of the subcontractors were common to all these prime contractors. Notable among these were the Greist Manufacturing Company, New Haven, Connecticut, suppliers of breech face pieces, striker pins, breech cotters, plungers, and catch plates for hand cocking; the Bard-Parker Company, Inc., Danbury, Connecticut, manufacturer of hand cocking assemblies, double loading stops, retaining pins, axis bolts, and trigger pawls; and the Raton Manufacturing Company, Detroit, Michigan, producer of various type springs.

The program was characterized by the excellent cooperation of the prime contractors. They not only exchanged manufacturing, design, and engineering information but on many occasions there was an actual


exchange of material on a loan basis. This close relationship did much to speed the production of the vitally needed guns.

Improved Manufacturing Techniques

The Oerlikon gun as turned out by the Swiss company was a tailored job requiring a great amount of hand fitting during the many hours required for its production. In adopting the 20mm gun the Bureau realized that in order to fill the urgent needs for this AA weapon, it would be necessary to adapt its manufacture to production line methods. This expectation was soon realized for the prime contractors, working closely with Bureau experts, refined the gun and manufacturing techniques to such a degree that production was speeded at least 50 per cent.

Two points of engineering interest stand out in the manufacture of the gun parts — first, the high degree of accuracy to which practically every piece was machined; second, the great amount of stock



that was removed from the original forgings in order to obtain the finished designs. Some appreciation of this problem is gained from a study of the metal removed from some of the major parts. The breech case forging originally weighed 170 pounds, when finished it was whittled down to only 41 pounds. The gun barrel was received as a rough turned forging which weighed 88 pounds; when finished it weighed 37 pounds. The barrel spring casing, which covered the recoil mechanism and took up the terrific backlash of firing, once began as a 56 pound solid alloy-steel forging, machined down finally to 6 pounds.

The necessity of removing from 50% to 80% of the weight of parts by metal removal brought about a tremendous problem in machine time and equipment as well as costs. However, in the early days of the 20mm program the most important element was time. Accordingly, the Bureau and the prime contractors devoted their efforts to the two major aspects of the problem: the development of methods designed



to speed up metal removal; and simultaneously, the redesign of certain components to further reduce metal removal.

This campaign brought specific time and material savings which greatly increased production. The list of these improvements is too long to give in detail, but a discussion of a few illustrative cases will be sufficient to show the trend. As pointed out previously fifty pounds of alloy steel was machined from the barrel spring casing. A new design for this piece was perfected which consisted of a hollow forged base to which a tubular steel extension was welded, thus reducing the original weight from 56 pounds to 14 and effecting a corresponding savings in man-hours, machine tools, and cost.

Early practice was to make the trigger cover plate from a solid steel forging, weighing nearly 6 pounds which was whittled down bit by bit on a dozen machines In 29 operations. Engineers decided to stamp the plate out of a piece of steel with a giant hammer and to weld a small part, formerly forged.



This reduced operations from 29 to 15, saved 2 pounds of steel per piece, hours of machining, and 90% of the cost.

The 20mm hammer axis bolt, the piece that hit the shell, had a slotted head of elaborate shape, but it was redesigned as a simple, cone-shaped bolt which eliminated two operations and cut cost to about one-twelfth the original.

A typical example of time savings Is Illustrated by the reductions effected by Pontiac:

Part NameOriginalSept. 1-44Total
Breech Casing190.00 hours29.76160.24
Barrel 37.075.4231.65
Misc. Small Parts (Original 18) &
Gun Assembly
147.40 33.97113.43
Spare Parts  53.927.5746.35

Pontiac was the most aggressive of the prime contractors in reducing both the time and cost of


production but Center Line and the A.O.G. Corporation also contributed greatly in this effort.[41]

d. Distribution

During the course of the war the 20mm gun was the most active of the items on the Bureau's lend-lease program, roughly 15% of the total production being distributed through this source. The fact that the 20mm bulked so large under lend-lease is not surprising in light of the fact that the British set up in the American-owned A.0.G. Corporation the first facility In the United States for the manufacture of these guns. Of the 19,336--20mm singles transferred under lend-lease, the United Kingdom received 14,798, Brazil 413, Chile 100, China 52, Columbia 26, Cuba 12, Dominican Republic 6, Equador 6, France 691, Greece 57, Haiti 1, Mexico 32, the Netherlands 103, Norway 31, Peru 6, Russia 3,012, Uruguay 3, Venezuela 8, and Yugoslavia 9.[42]

No 20mm twins were transferred to a foreign government.



20mm AA Single Mounts Installed on US Navy Combatant Ships

  Percentage Distribution by Type of Ship
 Number of






July 1, 19400       
Dec. 31, 19437,44313%18%5%7%30%23%4% 
Dec. 31, 194412,42992045233153
Jun. 30, 194510,18092335203543
  20mm AA Twin Mounts
Jun. 30, 19452,3811514965015 



The tremendous number of 20mm guns installed on American vessels were distributed as follows:[43]

Number of 20mm Shingle and Twin Mounts Installed on US
Navy Combatant, Other US Navy, and Merchant Ships

 Number of
Percentage Distribution by
Vessel Categories
July 31, 194459,92117%38%45%
January 31, 194583,83315%45%40%
July 25, 194588,30312%44%44%
July 25, 1945



Training activities received 1500 single and 100 twin 20mm gun assemblies. There were only 10 twins sunk or destroyed in comparison with the 5,783 single assemblies sunk, destroyed, or scrapped.

The mounts Mark 2, 4, 5, and 6, amounting to 30,945 of the total procurement, were declared obsolete.[44]

e. Future of the 20mm Gun

An analysis of antiaircraft action compiled by the Commander-in-Chief, United States Fleet, showed that over the period from December 7, 1941, to September 1944 the 20mm was the most effective of all antiaircraft weapons. On that date, 32% of identifiable "kills" had been credited to this caliber. This supremacy was not retained. Increase in range of attacks, shift of emphasis to night operations, increase in 40mm batteries, and extensive improvements in performance of 5" guns brought a



relative shift in effectiveness. The following table is illustrative of the change:[45]

Second half 194248.3%1.3%35%

Although the trend too larger calibers was pronounced, and there was even some advocacy for the complete removal of the 20's, it was considered that a wide field of action remained for the gun in countering surprise attacks, discouraging strafing, attrition to enemy aircraft at short range, and as a defense against flying bombs. Each of these functions demanded characteristics of reliability, high degree of mobility and large volume of fire-characteristics possessed in high degree by the 20mm.

While the 20mm gun proved very successful as a free swinging machine gun, its value was limited because of the short ranges within which it was effective. By the summer of 1945, however, the



policy of Installing 40mm at the expense of the 20mm had progressed to the point where the 20mm batteries were rather weak. To the Fleet the 40mm gun appeared to be the minimum caliber weapon capable of destroying a plane in a suicide attack. Changing enemy tactics and increased volume and accuracy of the 40mm continued to reduce the comparative effectiveness of the smaller gun to the point where a large battery of them was neither necessary nor desirable. However, there were two major reasons for the retention of a minimum battery of 20mm guns: first, the independence of a power source of operation, and second, the fact that it could be put into action faster than the larger power-driven calibers. Nevertheless, at the end of the war the demand for the 20mm was only for those locations where space or weight limitations did not permit the installation of 40mm batteries.[46]



free swinging gun. At the end of the war the design had not been perfected but experiments had demonstrated that the new gun would fall in a category between 30 and 40mm. In September 1945, $650,000 was allocated to finish the project. In this connection it is interesting to note that the 20mm single mount was originally considered to be the largest machine gun that could be handled by one man as a free swinging mount.[47]



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Transcribed and formatted by Thomas Wildenberg, HyperWar Foundation