40mm Bofors Gun

Chapter VI

a. Introduction

The 40mm Bofors antiaircraft machine gun has had a short but vital history in the U. S. Navy. First Installations afloat were made In the early summer of 1942. Since that date, Bofors guns have been placed on virtually all combatant ships and on most non-combatant vessels large enough to support the weight of a 40mm assembly. In defense against low-flying enemy aircraft, the 40mm has had the task of spanning the relatively large gap between the 20mm AA gun and the larger 3" and 5" DP guns. In that role, the Bofors has become the very "backbone" of our close-in AA defense.

The design of the Bofors 40mm appears to have originated at the Krupp Works in Germany shortly after the end of World War I. then the provision of the Versailles Treaty necessitated the discontinuation of Krupp operations In Germany, Otto Krupp obtained a block of stock in the Swedish Bofors Company, and Krupp equipment along with key personnel was moved




to Sweden. In time the Germans achieved full control of the company but were eliminated by a Swedish law in 1930 which prohibited foreign ownership of munition factories. Controlling Interest in the company was purchased by Axel Wenner-Gren, a Swedish international financier. The Bofors 40mm gun, like other Bofors products, was sold to various countries and gained a high reputation for efficiency during the Spanish Civil War.

b. Adoption of Gun by U. S. Navy

1. Critical Antiaircraft Situation

The 40mm Bofors gun story can be understood only In terms of the critical antiaircraft situation which existed in the Navy at the time of the gun's adoption and early manufacture. The development of the airplane as a threat to the existence of the surface ship is too well known to warrant repetition here, but the antiaircraft activities within the wavy in 1940, and even earlier, should be recalled in order



to appreciate the pressure under which the Bofors came to be a U.S. Naval gun.

In recognition of the growing necessity for antiaircraft fire, the more or less continuous Bureau of Ordnance experimentation with double purpose guns in the 1920s finally culminated in the early 1930!s in the development of the 5"/38 DP gun which has fulfilled its purpose throughout the war to the complete satisfaction of all concerned -- a rare testimonial for any ordnance equipment in anyone's Navy- or Army. While the longer range AA gun field was thus taken care of, except for insufficient numbers, the situation was far from satisfactory in the short range category. Neither the .50 caliber machine gun, effective enough in plane-to-plane fire at point blank range, nor the 1.1" gun which the Bureau of Ordnance had developed in quadruple mounts in the 1930's were competent to meet the menace of the Second World War plane. The l.l" was too heavy to serve as a "last ditch" free mount and too light to span the gap between itself and the 5 Inch guns, even had all the l.l" "bugs" been eliminated. The lack of adequate



short range AA guns together with Insufficient quantities of the best guns then available created a situation by 1940 which can hardly be termed anything but critical.

In the spring of 1940 the Secretary of the Navy designated Rear Admiral (later Fleet Admiral) E. J. King to make special studies looking toward the improvement of antiaircraft batteries, and on August 9, 1940, the Chief of Naval Operations created the Navy Department Anti-Aircraft Defense Board with Captain W, A. Lee, Jr., USN, as Senior Member, for the purpose of conducting a continuing study of all phases of antiaircraft defense.[1] The recognized urgency of the AA situation can be seen clearly from reports made by Admiral King and the AA Board. In a report to the Secretary of the Navy, Admiral King stated: "It appears clear from the data available that ordnance material - armament and equipment--is the 'bottle-neck' for the work In hand and,



consequently, that steps towards the elimination of this bottleneck are urgent and immediate."[2] And in the Antiaircraft Defense Board's report of December 26, 1940, the following declaration is made: "The Navy Department Antiaircraft Defense Board considers that the lack of adequate close range antiaircraft gun defense of existing ships of the Fleet constitutes the most serious weakness in the readiness of the Navy for war."[3]

In the Bureau of Ordnance, a variety of vigorous steps were being taken to meet the recognized deficiencies. These steps included stepping-up the manufacture of the 1.l" until such time as a more suitable battery could be substituted in adequate quantities, efforts to improve AA fire control, studies relating to the increase of numbers of AA guns on board combatant and other ships, and steps to procure more effective guns in both the 20mm and



40mm calibers. On July 15, 1940, Captain (later Rear Admiral and Chief of the Bureau of Ordnance) W.H.P. Blandy reported to the bureau and was detailed to coordinate the whole antiaircraft ordnance program. Captain Blandy was, incidentally, one of the original members of the Wavy Department Anti- Aircraft Defense Board.[4]

2. Purchase of a 40mm Bofors Gun

There are several threads to the Bofors story prior to the establishment of manufacturing facilities and the Navy's purchase of manufacturing rights from the Swedish Bofors Company, but the first thread to follow is the purchase by the Bureau of Ordnance of a twin 40mm Bofors gun and mount which arrived on the AMERICAN LEGION in New York on August 28, 1940. The twin, equipped with standard sights, and accompanied by spare parts and 3000 rounds of ammunition, was shipped to the Naval Proving around at Dahlgren



where exhaustive tests were made for comparison with other available AA guns which resulted In the Navy's decision to adopt the Bofors.

Rear Admiral W. R, Furlong (Chief of the Bureau of Ordnance 1937-1941) first became particularly Interested in the 40mm Before gun in the fall of 1939 through Mr. Henry Howard, an engineer and businessman of Newport, Rhode Island.[5] Mr. Howard was a delegate In June 1939 to the International Chamber of Commerce Convention in Copenhagen and from there went to Stockholm. Through the intercession of friends, he was able to examine the Bofors 40mm and



witness a firing demonstration.[6] On the return to this country, Mr. Howard sought out Admiral Furlong and gave him a description of the gun together with some information regarding the methods of fire control which he had seen. Although there had been some earlier knowledge of the Bofors products in the Bureau, it was apparently as a result of the above conversation that Admiral Furlong in October 1939 directed Sections "K", "T", and "M" to make special studies of available Bofors literature looking toward the purchase of the Bofors AA gun. Two of the sections recommended the purchase.[7]

Just at the time that Interest in the purchase of a Bofors gun was being aroused In the Bureau, the York Safe and Lock Company of York, Pennsylvania, was



becoming interested in obtaining manufacturing rights for the gun in this country. Presumably the interest of the company had been stimulated through a visit by Mr. J. A. Cunningham, Assistant to the President of the Company, to Sweden where he, like Mr. Howard, had witnessed a demonstration of the Bofors AA gun.[8] On November 10, 1939, Admiral Furlong replied to an inquiry from the Company concerning the Navy's attitude to the Company's acquisition of Bofors manufacturing rights that no objections would be raised and suggested that any agreement should Include the right to manufacture for the US Government in the event the guns should be wanted. He also expressed the desire to purchase one of the 40mm guns for test purposes.[9] The plan for the York Safe and Lock Company to acquire manufacturing rights progressed to the point where a representative of the Company, with Naval authorization, started for Sweden In April 1940



to negotiate a contract. Just as the representative was ready to sail from New York, however, the Nazis seized Norway and plane for the visit were dropped.[10]
Negotiations for the purchase of the twin gun continued, however, through the Naval Attaché in Stockholm, and the purchase of an air-cooled, rather than the desired water-cooled, twin mounted gun was completed in July.[11] Eventually arrangements were made through the State Department for transporting the gun across Finland to Petsamo where it was shipped on the AMERICAN LEGION, arriving in the New York



harbor in late August 1940.[12] Mr. K. E. Jansson, a Before engineer who participated in the tests of the gun at Dahlgren, accompanied the shipment.

3. Testing Period

Prior to the arrival of the sample Bofors gun, Admiral Blandy (then Captain) and Captain A.F. France (then Lieutenant Commander), Chief of the Bureau Fire Control Section, flew to Trinidad in August to inspect the German fire control system for the 40mm Bofors which the Dutch had installed in H.N.M.S. VAN KINSBERGEN. The Dutch fire control system and the opportunity for inspecting it were suggested by the Dutch Naval Attaché in Washington, Captain (later Admiral) Ranneft. Since there were no aerial targets available for testing the system, the Chief of Naval Operations boarded the cruiser TUSCALOOSA to Trinidad from Guantanamo, Cuba, 1500 miles away, in order to




have planes to tow the targets. "The demonstration was about as International an affair as it could be. American planes towed targets for a Dutch ship firing Swedish guns with a combined Dutch-German fire control system, the whole taking place in the Caribbean Sea off a British port."[13] While the American Naval observers were not particularly impressed with the Dutch fire control system, they returned full of enthusiasm for the Bofors gun.

The first tests of the gun which Admiral Furlong had obtained from the Bofors Company were conducted at Dahlgren on September 28, 1940, with representatives present from the Bureau of Ordnance, the Army Ordnance Department, and the Naval Gun Factory. The results, of these and later tests convinced virtually everyone of the superiority of the 40mm Before gun over all other guns of its general class, which were being studied at the same time.[14] Among the machine guns



heavier than the l.l" which were being considered were the US Army 37mm and the British Naval 40mm pom-pom, with the choice soon narrowing down to the Bofors and the British pompom The British were extremely anxious to have us adopt their gun, and the fact that British aid would be readily and immediately available in initiating manufacture was put forward as an argument in favor of its adoption. The pompom, moreover, was giving a good account of itself on British ships. On the other hand, there was the distinct disadvantage that the pompom was designed for cordite powder, which if the gun were accepted, would either require the development of manufacturing techniques and facilities or result in an undesired dependence upon the British for necessary powder supplies. After thorough study it was found that the gun was not susceptible to conversions which would permit the use of American powder. Also there was the consideration of muzzle velocity: the pompom had a relatively low velocity, 2350 f.p.s. as compared with 2830 f.p.s. for the Bofors 40mm. The success of the pompom in action




was more than offset by the proved qualities of the Before in the hands of a number of powers who were using it. The British Army had already adopted the Before and shortly after our decision in favor of it, the British Naval officials also decided to undertake production of the gun.[15]

Immediately upon his return from Trinidad, Captain Blandy requested the Dutch Naval Attaché to take steps to obtain the drawings and specifications for the gun, mount and fire control equipment. Holland had been occupied by the Germans and the Dutch Admiralty had not been able to remove drawings to London. Fortunately there were prints In Surabaya, Java, which were microfilmed and sent to, Washington. Work was started immediately on the translation of the prints from Swedish and Dutch to English and on the conversion of dimensions to



American measurement and standards. In January 1941 additional drawings were obtained from the British through Captain C. S. Miller, R.N., of the British Admiralty Technical Mission located In Ottawa, Canada. The British Army, Incidentally, was beginning to manufacture the Bofors at the Autism Fensom Company of Hamilton, Ontario, Canada. They were in full production In January 1941 with gun barrels and were laying out their factory to produce the complete gun.[16]

While the Interest of the US Army in the Bofors gun had no bearing upon the Navy's adoption of the gun.[17] It should be noted that Army Ordnance officers became Interested in the gun at least as early as 1937. The Army, apparently, became interested in procuring a gun for test purposes somewhat after efforts in that direction were initiated by the Navy. In November 1940, a British Army 40mm Bofors with single



mount was obtained by the Ordnance Department, and tests of this gun were witnessed by Naval Ordnance personnel just as Army officers were witnessing the naval tests, by January 1941, the Army had obtained drawings which they turned over to the Chrysler Corporation of Detroit for conversion to American measurements. In both the negotiations for manufacturing rights and in the establishment of manufacturing facilities, the Array and Navy cooperated to the advantage of both services.

Chronologically, the next chapter in the history of the Bofors gun concerns two main developments which progressed concurrently: the working out of plans for the establishment of manufacturing facilities, and negotiations with the Bofors Company of Sweden for US rights to manufacture the gun. Since the establishment of production is a continuing story, the negotiations fill be treated first.

4. Negotiation of Contract for Manufacturing Rights

The negotiations between the Navy Department and Bofors Company for US manufacturing rights to



the Bofors gun resembled negotiations which commonly characterize a difficult international political compact far more than those which usually accompany a commercial agreement. Although the 40mm gun was decidedly a "or sale" article, already in the hands of numerous powers other than Sweden, the complexities arising from Europe's state of war together with the then US role of "arsenal of democracy" added varied difficulties which in more normal times might not have existed. Perhaps the most difficult point raised was the Swedish Government's request, in return for its consent to US manufacturing license, for certain US airplane export and manufacturing licenses to which the US government would not agree. The eventual withdrawal of these demands by Sweden made possible the conclusion of a contract which was signed on June 21, 1941.

Prior to the entrance of the Swedish government into the picture, however, the decision had been made by the Bureau of Ordnance to adopt the gun, and negotiations for manufacturing rights had been



initiated with the Before Company through Lieutenant Commander (later Captain) W. L. Heiberg, USN, then US Naval Attaché at Stockholm. The Before Company offered manufacturing rights for the naval type gun and mount together with shop practices and the services of two engineers for $600,000. For an additional $250,000 they offered also manufacturing rights for the Before 40mm ammunition. Subsequent to the commencement of the negotiations, it became evident that the US Army was also interested in adopting the gun, and it was agreed that the Navy should carry on the negotiations for both services.[18] To some degree this complicated the issue in that the Bofors field carriage in which the Army was interested was the one item on which there was a US patent.

Subsequent to the Navy's decision to adopt the Bofors gun, the Swedish Legation in Washington sent a representative, Captain Weasel, to Admiral Furlong to outline the requests which Sweden intended to present.[19] When in response to an inquiry by the Chief



of the Bureau of Ordnance It was learned that the Army Air Corps, and to a somewhat lesser degree the Bureau of Aeronautics, were unwilling to agree to the concessions requested by the Swedish government.[20] All of the Items which the Swedish government listed as compensations for granting permission to a contract with the Bofors Company pertained to aeronautical material and particularly to manufacturing rights for specified United Aircraft Corporation engines and Republic Aviation Corporation planes.[21]

The Impasse in the negotiations with Bofors lasted until late in April when the Swedish government agreed to withdraw its demands. The probable reasons for the withdrawal were: first, the Swedish government discovered that the Bofors items, save one, were not patented In the US, a fact which they apparently did not previously know; and, secondly,



they learned that both the Navy and Army Intended to proceed with the manufacture of the gun whether or not agreement was reached with the Before Company.[22] Although the Swedish government receded from its previous stand in its quid pro quo requests with reference to the Bofors manufacturing rights, It continued to press the US government for the desired licenses "In the spirit of mutual good will." Previous services of the Swedish government to the United States, including among them cooperation In the purchase and shipment of the Bofors twin gun In the summer of 1940, together with other diplomatic considerations, led to a reconsideration of several of the earlier requests and to the granting of the manufacturing license for Republic Aircraft Corporation's frames.[23]



With the resumption of negotiations between the Bofors Company and the Bureau of Ordnance, the agreement envisaged was one which would cover not only the Naval type of gun and mount, together with ammunition, but also the Army type gun and field carriage, the field carriage being covered by US Patent 2,103,670. The terms finally agreed upon were $600,00 for unrestricted rights to make or have made in the United States, and to use all of the material mentioned, for gun and tool drawings, and plans regarding shop practice. Also the services of two production engineers were promised for the period of one year. The considerations which made the agreement appear advantageous, not to say necessary, were succinctly stated in a letter from the Chief of the Bureau to the Secretary of the navy on May 29, 1941:[24]

(a) The services of engineers with experience in the production of the Bofors guns and mounts can reasonably be expected to provide the most valuable insurance against.



costly errors and delays in manufacture; no engineers with experience in production of this material are now available in the United States.

(b) The plans obtained from the Dutch Navy do not include manufacturing drawings, tool drawings, shop procedures, and various related manufacturing aids which it is now desired to obtain from the Bofors Company; these are considered of great value in ensuring expeditious and. Successful manufacture
of the Bofors material in this country.

(c) Although of the five Items covered by the proposed agreement (viz., naval type gun, naval twin mount, army type gun, army field carriage, and ammunition for both types of gun) only the army field carriage is patented, even the entire amount to be paid is considered inexpensive Insurance against such claims as might eventually arise from as yet undisclosed rights connected with the presently unpatented items. In this connection It is noteworthy that an expenditure of $250,000,000 to $300,000,000 will be involved in the manufacture of the naval type gun and mount, and ammunition.

(d) A contract for the purchase of one Bofors twin mount, with guns and ammunition, for test by this Bureau, negotiated between the United States Minister to Sweden and the Bofors Company In July 1940, stipulated that that contract did not grant the United States a license to manufacture Bofors equipment. Acceptance of the test gun under these conditions makes it advisable to obtain manufacturing rights, irrespective of the now existing patent situation as far as it is known.



In the contract (N557a-2) which was signed at Stockholm on June 21, 1941, with the US Naval Attaché representing the Navy Department and Captain Oscar Linden the Bofors Company, all manufacturing rights for both Army and Navy equipment together with drawings of operating and measuring tools and descriptions of shop practices were included.[25] The total price agreed upon was $600,000, of which the Army was to pay one-half, but $100,000 of this amount was contingent upon the arrival in the US of two Bofors production engineers. Since these men never arrived, the total payment was reduced to $500,000.

From the viewpoint of possible future complications, the most important feature of the contract concerned the wording which related to the use to which material manufactured under the license might be put. In other words, did the contract cover, In addition to use by US armed services, the right to export Bofors guns under Lend-Lease or similar



arrangements? Great care had been exercised in the drawing up of the contract to limit the use of items manufactured as a result of the contract to US forces only. The original wording suggested had, in fact, been changed from "for United States Forces only" to "for United States use.":[26]



Subsequent to the execution of the contract, however, the Before Company expressed concern as to the interpretation of the term "for United States use." A representative of the Before Company, in the person of Captain Harvey Combe (a British subject and ex-British Army Officer) arrived in the United States prior to the completion of the contract, but negotiations were nevertheless completed in Stockholm. Later Before requested Combe to negotiate such further agreements as would be required to cover all contemplated uses of Bofors equipment to be manufactured in the United States. After requesting an opinion from the Judge Advocate General of the Navy, the Navy Department decision was that further negotiation was unnecessary. The following excerpt from the Judge Advocate General's opinion Is quoted as stating the Navy views:[27]

.... It is the opinion of the Judge Advocate General that the expression 'United States use'



appearing in Article 1, section (a) of the subject contract ... as properly interpreted means use in defense of the United States. As so construed, the employment of materials covered by the contract, in furtherance of or in accordance with or to carry out the provisions of the defense aid Act (Public Law 11 -77th Congress) entitled 'An act to Promote the Defense of the United States' constitutes an authorized use within the terms and provisions of such contract.

a. Production Program

1. Early Design Problems

It should De emphasized that while the basic twin Bofors gun and gun mechanism were obtained from the Swedish Bofors company, the U. S. Navy Bofors gun and associated equipment is actually a very different final product from the original. The Swedish Bofors was manufactured in single and in twin mountings, both manually operated. The US Navy adopted twin and quadruple mounts, both operated by power and associated with gun directors, which presents quite a different picture from the parent Swedish gun.[28]



Obtaining Bofors drawings and manufacturing rights was, then, merely the beginning of the Before story.

The design for the quadruple mount was worked out by Section "T" of the Bureau of Ordnance according to a plan suggested by Mr. George A. Chadwick, then Chief Engineer of the Bureau.[29] In order to save time which would have been required for designing a completely new mount, the quad mount was in principle two twine on a single mount leaving room for the loaders between the pairs of gun mechanisms and giving the appearance of two sets of twine rather than a single mount.

The first design problem which had to be solved was that of converting drawings which had been obtained from the Dutch, the Bofors Company and the British to American measurements. The conversion Introduced manifold difficulties. When changed from the metric system, a great many of the measurements



became troublesome decimals which added complications to the matter of tolerances. Worse still, the dimensions called for in the drawings did not agree in many instances with actual measurements taken from the gun since certain dimensions allowed for hand working. All of the first guns had to be finished by hand due to improper clearances. There were notes on the drawings which read "file to fit at assembly" or "drill to fit at assembly" which told a story of careful, expert European workmanship In producing handmade guns, but which constituted nothing but headaches for American producers who were soon faced with the necessity of setting up assembly lines for mass production.

The task of translating the drawings and of establishing standard Navy drawings was turned over to the York Safe and Lock Company to which Mr. Chadwick was sent to render aid. The York Safe and Lock Company translated in terms of decimals whereas the Chrysler Corporation, which had in the meantime



accepted a similar assignment from the Army, translated in terms of fractions which complicated to some degree the program of arriving at interchangeability of parts "between the Army and Navy mechanisms. Something of the size of the task of converting the measurements can be seen from the fact that 8505 man-hours were required at the Chrysler Corporation to transpose the drawings from British to American standards.

2. Overall Procurement Program

(a) Initial Procurement Plans. 1941

The York Safe and Lock Company which had been interested in producing the 40mm gun more or less from the period when the gun was first considered, was chosen as the prime contractor for the guns and mounts. The choice was not made without expression of trepidation of the part of some of the officers in the Bureau, but it was extremely difficult at the time to interest private contractors in ordnance production and there was then no way of visualizing the magnitude of the program. The first official



commitment authorizing the establishment of facilities was made by letter of intent to the York Safe and Lock Company on February 19, 1941. Early plans called for the production of 500 twin mounts and 500 quad mounts, together with the guns with delivery of one quad and one twin in October 1941, increasing gradually thereafter to 25 each per month by May 1942.[30]

Since additional guns were needed in order to meet Lend-Lease requirements for the British, letters of Intent for establishing additional facilities were issued in April 1941 to the Blaw-Knox Company of Pittsburgh and the Chrysler Corporation of Detroit. These companies were selected on the recommendation of the Office of Production Management, and the plan was for Blaw-Knox to produce the mounts in a rehabilitated plant at Martins Ferry, Ohio, for which Chrysler would supply the guns. Chrysler had previously accepted proposals from the US Army to



produce air-cooled guns for the US and British Armies under lend-lease. The Navy, however, took over the administration of Chrysler production for both Army and Navy. York Safe and Look planned from the beginning extensive subcontracting for parts, and Chrysler planned to spread its work through a number of its plants and to contractors. Barrel forgings were to be obtained for machining by York Safe and Lock and the Naval Ordnance Plant, South Charleston, from Crucible Steel Company and Midvale Company. The Crucible Steel Company was, incidentally, already producing barrel, breech block and breech ring forgings for Otis Fensom in Canada. Somewhat later the National Supply Company also began to produce forgings. The Standard Machinery Company and the Kaydon Engineering Corporation became the prime contractors for roller bearing assemblies.

b. Development of the Procurement Pattern

Forty millimeter procurement throughout the war was one of the major ordnance procurement programs. From the original contracts in April 1941 which



called for an ultimate total of 500 twins and 500 quads for Naval use plus an additional 500 twins and 300 quads for Lend-Lease, the program has expanded until by the end of the war more than 2300 quads, almost 10,000 twins, and over 10,000 single joint had come off the production lines.[31] At the end of 1944, 40mm production together with 20mm, 3"/50, and 5"/38 gun production represented over 95 per cent of the value of the total gun and mount program.

Throughout the war, demands for 40mm guns increased constantly. The introduction of new or changed methods and weapons by the enemy as well as the changing tactics of war inevitably forced alterations of many ordnance products; in some cases they necessitated abandoning items; they did nothing, however, but increase the demands for 40mm guns, While these facts constitute a remarkable tribute to the gun, they also point up the vital character of the program for procuring it.



Forty millimeter guns and equipment were produced almost entirely by commercial manufacturers, very few of whom had had any previous experience with the production of ordnance materials.[32] They have, of course, had to run the gamut of problems which face commercial manufacturers when they attempt to meet the close tolerances and rigid specifications which must characterize the Navy's fighting equipment. In meeting schedules, 40mm manufacturers brought to the problem American industry's ingenuity and assembly-line technique. The number of instances of improvement in manufacturing methods, of redesign in order to produce a better part or to save man-hours in production are legion. At the Chrysler Corporation, to cite one example, the redesign of ten items saved 7,500,000 pounds of material and 1,896,750 man-hours in a year's production and at the same time released thirty-odd machines for the production of other parts.



The general pattern of the procurement program was one of few prime contractors and relatively large numbers of subcontractors. The York Safe and Lock Company subcontracted the major portions of Its work, the proportion running on some assemblies as high as 90 per cent. In 1943, York Safe and Lock listed 481 subcontractors and Blaw-Knox 200. The number of prime contractors producing components, other than for power drives and directors, never reached more than 20. In the main, the expansion was accomplished by more extensive subcontracting and by more efficient use of facilities originally allocated. In the production of mounts, for example, ultimate production schedules called for a twelve-fold increase in the output of twins and a twofold Increase In the production of quads. Chrysler production of gun mechanisms was Increased tenfold, an expansion made possible by an Army cutback of 40mm single mechanism production In January 1944.

Major shifts in the allocation of contracts to the major producers have been few though several have



been quite significant. The York Safe and Lock Company was gradually relieved of some of its more important functions in the program, including the transfer in July 1943 of its cognizance of 40mm gun and mount drawings to the Naval Gun Factory and the transfer of its prime contract for power drives to the Webster Electric Company of Racine, Wisconsin. Webster Electric had previously, as a subcontractor for York, produced approximately 90 per cent of York's power drive equipment.[33] Also in the procurement of power drives, a major change was made when the Ford Instrument Company, one of the original contractors, ceased in May 1943 to produce drives and Vickers, Inc., of Detroit was brought Into the program, Vickers and the Ford Instrument Company both being units of the Sperry Gyroscope Company.

There have been few radical changes in 40mm mounts, the differences in mods arising primarily



from the different drives used on the mounts. The only significant departure from the early mount design has been the adoption of a light-weight quad mount developed by Northern Ordnance, Incorporated, Minneapolis, Minnesota. The quad mount Mark 4, powered by a General Electric drive, is 1,000 pounds lighter than the Mark 2. In addition, some 2,500 pounds of electrical equipment, Including the amplidyne motors, are stowed below decks. This makes the mount assembly about 3,500 pounds lighter, which represents a considerable reduction in topside weight affecting ship stability. Approximately one hundred of these mounts had been manufactured when hostilities with Japan came to an end.[34]

The cost of 40mm assemblies was gradually but consistently reduced as the program expanded. The complete story would require a breakdown of the cost into individual components and the savings made through renegotiation of contracts and shifts from



higher cost to lower cost producers which is hardly warranted for the purposes of this account. Some conception of the general picture can be seen from the reductions made in estimated average costs of complete assemblies as given in the following table which includes spare equipment and is based through-cut on quad and twin equipments with hydraulic power drives:

40mm Quad $86,900$73,100$67,520*
40mm Twin$62,300$46,140$643,640
40mm SingleProcured from Army$9,500$9,500

*Actually the lighter mounts procured in 1945 cost considerably less, but the cost of the heavier mounts is given for purposes of comparison

Production was slower in getting started than had been anticipated; a pilot twin model was completed by York Safe and Lock In January and the first



quad in April. Blaw-Knox initiated delivery with two twin mounts in May. 3y the end of 1942 a total of 212 quad assemblies and 503 twins had been delivered. The peak month of twin productions was February 1945 and of quad production June 1945 when 550 and 142 assemblies, respectively, came from the producers.

The following table shows yearly production of completed equipments:[36]

Quad 212530744967

3. Associated Equipment

(a) Power Drives

The production of power drives was one of the major bottlenecks in the 40mm program. A slowly increasing rate of production, adequate for the first



months of the war, gradually fell behind a rapidly increasing demand until by the summer of 1943 guns and mounts in increasing numbers were going into storage for lack of drives. A vigorous reorganization of production facilities resulted in a greatly increased output; monthly schedules were met, the backlog of stored mounts was gradually absorbed, and by 1945 production was running well ahead of requirements.

In order to avoid delay in distribution of 40mm equipment to the Fleet it was necessary to adapt or modify power drives that had been developed for other gun mounts. The electro-mechanical power drive Mark 2 developed by the Ford Instrument Company for twin mounts was a modification of the 1.1" drive Mark 1; the General Electric Company's amplidyne drive, also for twin mounts, was an adaptation of the 1.1" Mark 2; and the Mark 5 developed by the Sperry Company for the quad was a direct outgrowth of the drive that had been designed for the Army's 90mm AA gun mount.[37]



A prime contract for the production of the power drive Mark 2 was placed with Ford Instrument Company In March 1942. This contract incorporated a major portion of the letter of intent issued to Ford In June 1941 for the manufacture of a power drive for the 1.1". It was not until June 1942 that the first Mark 2 was delivered.[38] The Ford drive proved unsatisfactory for service use due to frequent failures in the magnetic clutch-type transmission and in the limit stops. Production of the drive ceased in May 1943, when Ford completed its contract with the delivery of the 466th unit.[39]

The failure of Ford Instrument Company to produce a satisfactory product left but two sources of power drives in production, namely, General Electric Company, producing the twin Mark 4, and the York Safe and Lock Company, manufacturing the twin Mark 5. Originally



developed for the quad mount, the Mark 5 proved lacking in power and was converted for use on the lighter twin.[40]

Even with Ford in the program, production of drives could not keep pace with other 40mm equipment. To assist General Electric Company in attaining an increased rate of production on the drive Mark 4, the Naval Ordnance Plant, Center Line, Michigan, began the manufacture of mechanical assemblies. Later Center Line became an assembly point for complete drives.

On June 2, 1943 the monthly rate of amplidyne drives from General Electric was stepped up to 230 plus 20 from Center Line. General Electric absorbed this demand by entering Into extensive subcontracting with the Warner-Swasey Company of Cleveland for the mechanical subassemblies and with the Otis Elevator Company for amplidynes for Mark 4 drives.

In the meantime, the York Safe and Look Company increased its monthly rate to 75, but unfortunately



at the expense of spare parts. In spite of this showing it was apparent that, due to the many unfavorable production factors at York, the handling of power drive production would in due time collapse. It was felt that the Webster Electric Company of Racine, Wisconsin, principal subcontractor, was operating on a much sounder production basis and should assume the obligations of the prime contractor. The York contract was terminated late in 1943. Under the new contract, Webster agreed to produce 85 quad power drives per month and 150 twins.[41]

In a further effort to bridge the gap between requirements and production, the Bureau, late in 1943, placed a prime contract with Vickers Incorporated of Detroit for the manufacture of 1500 twin drives Mark 5. Vickers was ideally suited for this work since they furnished all hydraulic units for power drives Marks 5 and 6 and had Just completed delivery of 90mm drives of the same general type to the Army.[42]



The performance of the new contractors was excellent; within a few months, production schedules were being met and exceeded, and by January 1, 1945, there was actually a surplus of twin power drives.

The production of power drives for quad mounts, while generally tight and on occasions behind schedule, has presented no problems comparable to those of the twin program. The power drive Mark 5, originally intended for the quads, was replaced in early 1942 by the Mark 6 train (heavy duty). The Mark 6 contained much larger hydraulic units than the Mark 5, with consequent increased power, decreased maximum operating pressure, increased accuracy, and Increased ruggedness.[43] York Safe and Lock Company and the Webster Electric Company have been the prime contractors for these drives.

On October 25, 1943, Northern Ordnance was awarded a letter of intent for the production of complete quad



equipments. General Electric Company accepted a subcontract to design an amplidyne power drive for the new mount. The drive, as delivered in May 1945, is similar to the Mark 4 used on twins but with larger amplidyne generators and power motors.[44] At the completion of production of existing or completed contracts for twin and quad drives total deliveries will have been as follows:[45]

Ford Instrument Company466 
York Safe and Lock Company890780
Webster Electric Company2,3331,684
Vickers Incorporated1,338 
General Electric Company3,805 
General Electric Company--Warner Swasey1,700 
General Electric Company--NOP Center Line1,148 
Northern Ordnance, Inc. 900


Many of the bottlenecks and shortages in the production of power equipment arose as a result of the use of motors, bearings, and electronic items which could be obtained from only one manufacturer.



In the York type power drive the dither motor could be procured only from the Bodine Electric Company; the Federal Telephone and Radio Corporation was the only producer of selenium rectifiers, and for certain types of transformers the Thoradson Transformer Company was the only manufacturer. Each of these items caused delays in the 40mm mount program.[46]

The 40mm single mount, for installation on landing craft and other light vessels, was procured in large numbers from the US Army. The Army power drive was too light for control of the mount aboard ship where roll was encountered, and to overcome this difficulty the Massachusetts Institute of Technology developed a new drive, which was In the main a modification of the original Army drive. Its procurement was facilitated by the fact that the prime contractors, Westinghouse Electric, Williams 0i1-0-Matic Heating Corporation, and Gilbert and Barker Company, had all produced the Army type drive.


b. Fire Control

The 40mm story would be incomplete without some mention of the methods which nave been used for directing 40mm fire. In general, the Gun Director with which the 40mm quads and twins have served for most of the war was the Mark 51--a one-man, hand-operated director which has as its oasis the Gunsight Mark 14.

There are exceptions to the generalization, as 40mm guns were used with Gun Directors Mark 37 and 50, which are not primarily machine gun directors, and with early blind firing directors which for one reason or another were discarded. Also, beginning in 1945r the continuous efforts to make available to the fleet effective blind firing machine gun directors began to Dear fruit. Gun Directors Mark 57 and 63 began to be available early in the year and the third new director, the Mark 60, was nearing the production stage at the end of the war.

The Gun Director Mark 51 grew out of the development of the "Draper" Gunsight Mark 14 which has been


the inseparable associate of 20mm guns. One of the motivating reasons, in fact, for sponsoring the Gunsight Mark 14 was the thought that it might form the basis if a simple machine gun director. So serious was the need for such a director that, on the recommendation of Captains E, E. Herrmann and M. E. Murphy (then Commander), Admiral Blandy approved on January 16, 1942, a production program of 1000 directors while the instrument was still in the design stage. The first director was proved at Dahlgren May 4-7, 1942, and by June deliveries were being made for installation afloat.[47] This is perhaps the fastest design and production job of a reasonably complicated mechanism which the Bureau has recorded. By the end of 1942, a total of 723 directors had been produced, and by the end of May 1945 roughly 13,500.[48]

The Gun Director Mark 51 met what was perhaps the most critical need of the Fleet at the time of


its development. Its continuing usefulness is shown by statistics compiled from recent action reports which indicate that guns controlled by this director are still responsible for a large number of kills.[49]

Quad and twin 40mm mounts were also equipped with Gunsight Marks 3 and 4, respectively, for use in the event of power failures which would necessitate manual operations. Single mounts which were not equipped with power drives were initially supplied by the Army with cartwheel and fence type sights though a ring sight was developed for this mount and modifications made for anti-personnel firing. Single mounts for use on submarines were also provided with panoramic telescopes.

c. Ammunition

Beset by numerous difficulties in the early production stages which for a time threatened the entire program, the quality of the 40mm round was constantly


improved until today 40mm ammunition is a standard of excellence. Subsequent to January 1, 1942, over $600,000,000 was spent for 40mm ammunition and it is estimated that the total expenditure for this item exceeded that for any other type of close-in AA ammunition.[50]

At the very outset of the program for the development and production of ammunition components for the Bofors gun, the Army and Navy established the cardinal principle that the ammunition must be interchangeable as regards fit and effective use. The British round was adopted with the understanding that both services would be free to substitute components of proven reliability which would speed production.[51] The round developed by the Bofors Company was rejected on the ground that its fuze, which functioned on impact with rain drops, was too sensitive, was not bore safe and that It was not capable of mass production.[52]


The British round in many ways did not lend itself to quantity production, but the urgent need for this ammunition did not permit the usual careful research and development that generally preceded service issue.[53]

The early days of development were hectic. Forty millimeter guns and mounts were rolling off the production line, but no safe ammunition was available.[54] Of the several components, the original British fuze and the self-destroying type tracer probably proved to be the most troublesome.[55] The fuze Mark 27 developed by the Naval Ordnance laboratory, and the perfection of the tracer Mark 11 solved these difficulties.[56]


Early in 1943 the overall requirements for 40mm ammunition ware established at 5,250,000 rounds per month. From this beginning requirements were gradually Increased to a maximum of 12,000,000 rounds per month In the winter of 1944, Later developments resulted In a reduction to 4,500,000 rounds a month. The cutback was of material benefit to the rocket and high capacity ammunition programs.[57]

The entire loading program was carried by Triumph Explosives Incorporated until December 1942. It was realized that one contractor could not meet the demands of the 40mm program and the Navy, shortly after Pearl Harbor, began the construction of a model 40mm loading plant at Charlotte, North Carolina. A contract was negotiated with the US Rubber Company to manage the new activity, and on 21 December 1942 the plant was officially opened. It is significant that the rated capacity of Charlotte was exceeded within a year after operations began with no increase in the original building facilities.[58] In 1943, when


requirements were greatly increased, a supply contract was placed with National Fireworks, Inc. In spite of the efforts of these companies, increased loading requirements could not be met, and early in 1944 it became necessary to set up 40mm lines at the Naval Ammunition Depots at Hastings and McAlester. The reduction of requirements in 1945 allowed the Naval Ammunition Depots to concentrate on urgent rocket loading.[59]

4. Requirements

At no time after the beginning of production was there a comfortable margin of 40mm assemblies. Usually the situation was tight. A constantly increasing rate of production was necessary to keep abreast of requirements and to cut down an accumulating backlog.

Increasing estimates of requirements for twin assemblies were fairly constant while estimates for quad assemblies saw a certain amount of fluctuation. The problem which the bureau faced was one not only of increasing production but of meeting demands which varied tremendously over relatively short periods of


time. For example, estimates based on Chief of Naval Operations Directives in the twelve month period, April 1, 1943 to April 1, 1944, increased for quad assemblies required in 1944 by 44% and in 1945 by 257%. The estimates in the same period for twin assemblies increased 137% for 1944 and 300% for 1945. The charts on the following page show the estimated requirements as issued during this one-year period.[60]


40mm  Quad and Twin Assemblies Chart


Pyramiding requirements kept the 40mm program under forced draft. Assemblies were produced as rapidly as facilities could be made available, and the material scheduled and delivered into assembly lines. Even so, production could scarcely keep up with requirements, and for many months there was a deficit. There Is some truth in the statement that the schedules were ahead of production, rather than that production was behind the schedules.[61]

In June 1944 the 40mm program became a "Must" on the War Production Board's Production Urgency List.[62] The stimulus furnished by this action, coupled with more extensive subcontracting and a more efficient use of facilities originally allocated, gradually brought production and requirements Into substantial balance by February 1, 1945.[63] Increasing requirements for quads after February, however, ran ahead of production.


Requirements for spares presented a continuing problem. The original procurement plane for 40mm equipment envisaged that one complete assembly out of every five would be earmarked for spares; that for each mounted barrel there would be a 150% reserve and that there would be 30% additional gun mechanisms complete with barrels.[64] These reserves were never accumulated. During the initial stages of the war it was more important to insure delivery of material to new construction and ships requiring improvement of armament than to produce spares.[65]

Spares policy was revised by BuOrd Order 63-43, dated December 30, 1943. Under this order requirements were expressed in terms of the number of spare assemblies, and selected major subassemblies, that should be in distribution reserves by January 1, 1944, January 1, 1945, and thereafter, to support the equipments installed, on hand, and planned for procurement at the time the order was placed. This change resulted


in a considerable reduction in the 40mm spare requirements as the new policy took into account the fact that actual requirements do not increase in the same ratio as the number of equipments in service. Requirements for 40mm quads and twins included.[66]

(a) Distribution Reserve or Working Pool:
 Distribution Reserve
 1 Jan.
1 Jan.
Mount Assemblies(less gun mechanisms
and barrel assemblies):




Gun Mechanisms (less barrel assemblies)   

For multiple mounts (pairs)


(b) Replenishment Requirements:
 Replenishment Requirements
(Calendar Years)
Barrels (exclusive of water jackets, etc.)
and barrel assemblies:

For multiple mounts


As for spare parts for the 40mm AA twin or quad gun assembly, one vessel spare part set was procured


for each gun assembly; one tender spare part set for every 25 gun assemblies, and one shore-based spare part set for every 100 gun assemblies.

5. Special Problems.

(a) Continuing Design Problem

One of the more troublesome design problems was that of interchangeability of parts between the Navy and Army guns and even between the naval guns produced at York and those produced at Chrysler. It will be recalled that the Chrysler drawings were obtained by translating from British drawings while the York drawings came from the Dutch originals--a circumstance which led to problems in the matter of tolerances. These differences resulted in approximately 200 parts which were not necessarily interchangeable.[67] In time the whole problem was solved with complete interchangeability all around save for water-cooling, portions of the wavy gun which were not required by the Army and for approximately tan small items. Since Army and Navy mounts differ both in operational and


design requirements, attempts at uniformity for these items are unnecessary.

The maintenance of 40mm drawings by the York Safe and Lock: Company eventually proved so unsatisfactory that it seriously jeopardized the whole 40mm program. Dimensional errors were common, drawings were not kept up to date, and in some instances tolerances were not specified. According to estimates, not over twenty per cent of the drawings were completely dependable. Contractors complained constantly that they were a source of considerable trouble and confusion to subcontractors. This state of affairs constituted a serious handicap to the program for increasing production. In August 1943, cognizance of the drawings was transferred to the Naval Gun Factory.[68]

Over 2200 drawings were reviewed, by the Gun Factory and priority given to changes required to


facilitate production. Engineers from the Blaw-Knox Company, Martins Ferry Plant, and the Naval Ordnance Plant, York, were assigned to the Gun Factory for the purpose of speeding the work. By December 1944, the priority drawing revision had practically been completed.[69] Subsequently the maintenance of the drawings was transferred to the Naval Ordnance Plant, York, Pennsylvania.

b. Balancing Production

In any procurement system based upon the work of numerous contractors the matter of balancing production becomes of paramount importance. This was particularly true in the case of 40mm production because of the large number of parts involved. There are approximately 5000 parts in the quad assembly and about as many in the twin. The advantages, not to say necessities, which made the 40mm program one of many participating manufacturers are obvious. But equally obvious is the fact that the touch-and-go three year


race between production and schedules was one principally of balancing the production of the numerous components. Perhaps the best statement of the process was made by the Bureau officer who stated In one of his reports, "It still takes all the parts to make a complete assembly."[70]

Looking at the picture as a whole, the principal shortages which held back production were power drives and electronic equipment. Both quad and twin production suffered In 1944 from a shortage of selenium rectifiers, Thoradson transformers, condensers and synchros. In order to eliminate some of the difficulties in obtaining selenium rectifiers and Thoradson transformers, a new circuit was designed for the power drives Mark 5 and Mark 6.[71] For a time a shortage of hand wheel bracket assemblies threatened to become the bottleneck which would hold up twin assemblies. In late 1942 guns were the item of the assembly which


endangered the program.[72] Perhaps the most striking example of all such difficulties was the failure of York Safe and Lock Company in October 1943 to produce
a single assembly due to a shortage of approximately 25 parts.[73]

Thus the balance has always been more or less precarious. As one Report pictured the program in late 1944: "Any unforeseen difficulties, such as casting defect, strikes, delay in rolling schedules at steel mills, or for any reason whatsoever, the failure of single sub or sub-sub etc., contractor can at any time threaten the entire program and cause a serious backlog which may or may not be made up." But the report adds: "However, such exigencies are being and will continue to be overcome."[74]

c. York Safe and Lock Company

The 40mm production program depended heavily for its success on the York Safe and Lock Company, York,



Pennsylvania, and this company can with Justice claim credit for a number of valuable contributions to the program. As requirements mounted, however, it became increasingly clear that the company could not be counted on to carry the responsibilities which were essential to the continuation of its major role in the program. Previous mention had been made in this report of steps taken to relieve York Safe and Lock of its prime contract for power drives and to transfer the administration of 40mm drawings to the Naval Gun factory. On January 33, 1944, the Navy Department took over certain portions of the York Safe and Lock Company, consisting principally of the facilities known as the Special Ordnance Plant. The Special Ordnance Plant had been constructed at government expense of approximately $8,000,000 for 40mm production. On June 19, 1944, these activities were designated as the Naval Ordnance Plant, York, and the Blaw-Knox Company engaged as the contractor-operator.

The conditions which led to the necessity for the transfer were such as to threaten the 40mm program. The Bureau had entertained fears from the beginning



that too much dependence in the company rested on Mr. Laucks, the President. With the death of Mr. Laucks and a subsequent change in ownership of the company, involving highly questionable financial manipulations, the critical nature of the situation became more Intense. The most serious aspects of the problem were: (1) inefficiency evidenced in procurement of material and in stock control; (2) an excess of facilities and personnel as compared to other companies which were producing greater amounts; and (3) coats that were too high.[75]

In the period between January 23, 1944, and June 19, 1944, the York Safe and Lock Company was operated by the Navy Department with Captain D. F. Ducey, USN, acting for the Secretary as the Officer in Charge of the Plant. The Secretary was authorized to take over the plant by Executive Order No. 9416 of January 21, 1944. During the period of direct Navy operation and since the establishment of the



Naval Ordnance Plant, York, in June 1944, performance improved steadily. Overhead was decreased, scheduled production balanced, rejections decreased, and the performance of subcontractors bettered.

d. Machine Tools. Materials, and Priorities

At the beginning of the 40mm program the Navy's antiaircraft guns shared with guns for aircraft the top position on the priority list for new machine tools, in spite of this high rating, machine tools constituted one of the major problems of the program. The Bureau was frequently reminded by contractors that increased schedules could not be met without a corresponding Increase in facilities. In some instances installations could not be made for over a year after their scheduled deliver. Despite Bureau efforts to expedite deliveries, the machine tool industry could not expand its facilities rapidly enough to meet on time the tremendous demands made upon it by the Army and Navy.
In many cases the impossibility of obtaining the desired machines made it necessary to adapt existing



equipment for the required purpose. Through the ingenuity and resourcefulness of engineers and production experts, many machine tools were converted for new work. To name but three examples: a two-spindle machine was needed to drill, countersink and tap holes in both sides of the breech ring. To meet this need, tool engineers tied a vertical drilling machine In with a new tapping machine. In another Instance, an old hydraulic press formerly used to straighten rear axle housings was converted into a broaching machine for use on the breech block. One company resurrected a discarded planer type grinding machine and put it to work on the gun sight. Contractors were constantly on the lookout for changes in design which would affect a savings in machine tools and at the same time speed prodution. For example, by changing gun pawls from forgings to strip steel stampings embossed and line reamed, 13 machines were freed for other jobs. Originally the housing was cut from solid billets of steel but the substitution of forgings made possible the transfer of 17 machines to other critical work. Such illustrations could be multiplied many times. While these adaptations



contributed significantly to production, the bulk of the 40mm production came from Bureau procured machine tools.

The original Swedish drawings called for a variety of high alloy steels, medium alloy steels, straight carbon steels and non-ferrous alloys. The close chemical tolerances specified ruled out their use in the American 40mm gun since sufficient quantities for mass production could not be furnished. The substitution of one steel for another was carried as far as possible without affecting adversely the quality of parts.

Considerable savings were made in the conservation of critical and strategic materials other than in steels. When necessary to conserve tin, silicon bronzes were used in both castings and bar stock. A further attempt were made to save copper and tin by the substitution of malleable iron castings, but the experiment was not successful due to slow deliveries and the excessive machining operations required on the castings. The development of



steel cartridge cases provided a means of conserving brass.

Under the Priorities System In force during 1941, 40mm guns were assigned ratings ranging from A-l-2 to A-l-d, depending upon the vessel for which they were intended. Beginning with the Army and Navy Munitions Board Priorities Directive of January 13, 1942, the 40mm Program was assigned a blanket rating of A-l-a, the highest to which military production was then entitled. This too standing was retained in all subsequent priorities directives. Prior to February 1942, ratings were extended by preference Bating certificates countersigned by the Navy inspectors. After this date, manufacturers were permitted to extend the ratings assigned to their production without clearance, except for machine tools and capital equipment. Ratings on the latter could be assigned only by certificates countersigned by the inspector.

Under the Production Requirements Plan, which was first introduced in the second, quarter of 1942



and became mandatory in the third quarter, manufacturers applied to the War Production Board through their claimant agencies for a rating pattern and authority to purchase the necessary materials. In their applications, they were required to show the ratings from their customers and the quantities of material required for production. Review by the inspector prior to submission, which was a prerequisite of the Plan, saddled the inspectors with an almost impossible job because of the difficulty of estimating accurately the manufacturer's requirements for materials of all types.

The Production Requirements Plan was replaced by the Controlled Materials Plan in March 1943. With the Introduction of CMP, the controlled materials--steel, copper and aluminum--were ordered solely on allotments from the various claimant agencies. All other materials and fabricated items continued to be controlled by priorities. The allocation system of CMP somewhat eased the



critical condition of controlled materials and in general enabled 40mm manufacturers to obtain their requirements on schedule. The emphasis then shifted to the expediting of critical components and later to manpower. In June 1943 the 40mm program became a "must" on the Production Urgency List of the War Production Board. The "must" position was held until early in 1945 by which time manpower problems had been reduced to the replacement of labor lost by attrition.

d. Use and Performance

1. General Characteristics

The 40mm gun can be operated either fully automatic or single fire. In automatic, it is capable of a maximum cyclic rate of fire of approximately 160 rounds per minute. A unique characteristic of this gun is that the trigger mechanism controls the rammer operation only; once the ramming cycle is started, the round is loaded and automatically fired without further control.



The individual gun mechanisms are alike except for the changes necessary to make them right and left guns in the pairs. Conventional pedestal-type mounts, for both twin and quad assemblies, have power-operated elevating and training gear which position all guns as a unit both in elevation and in train. Originally the power drives were controlled either at the mount by means of the pointer's and trainer's handwheels, or from a director through an electrical-control system. Later mounts were provided with a single control lever, or joystick at the pointer's station which is used to control both elevation and train drive. This provides a unified and effective means for controlling gunfire, particularly when employing tracers. The twin mount weighs approximately 12,300 pounds while the quad weighs 22,500 pounds.[76]

The ammunition is of the fixed type, loaded into clips having a capacity of 4 rounds. Each



cartridge weighs 4.8 pounds and the projectile alone weighs slightly less than 2 pounds. Of twelve different types of 40mm ammunition which were produced, five types were in use at the end of the war: high explosive incendiary bright tracer, high explosive incendiary dark tracer, night explosive incendiary dark ignition bright tracer, armor piercing, and high explosive incendiary bright tracer non-self-destroying ammunition. The muzzle velocity of the projectile averages 2390 feet per second and the tracer burning time varies from 8.5 to 10.5 seconds depending; upon the ammunition type. This burning time gives an approximate range of 4200 to 4500 yards. A point detonating fuze causes high order detonation of the TNT projectile burster charge on contact with a target offering a resistance equivalent to or greater than 3/16" chipboard. In addition to TNT, the projectile contains a pellet of magnesium and aluminum powder which provides incendiary action. Smokeless powder is the standard for 40mm ammunition and approximately 3/4 pound is used in each round.



2. Distribution

Antiaircraft guns were mounted on combatant ships in such numbers that only weight and space consideration were limiting factors. When original limits were reached material already installed on topside was removed to make available more capacity for more antiaircraft guns. In this program, the 40mm quads were, In the main, installed on battleships, cruisers, and carriers. Due to their lighter weight, twins had a considerably wider distribution on lighter combatant ships and on numerous non-combatant vessels. The single mount has been distributed to destroyers, destroyer escorts, submarines, and landing craft.

The U.S.S. WYOMING received the first quad on June 22, 1942, and the first twin was installed on the U.S.S. COGHLAN on July 1, 1942.[77] Of the first
quads, 12 were allotted to AA training centers and Schools, 36 to the Pearl Harbor Pool, 2 to lend-lease and 43 for installation on the following ships:





The first 187 twins were distributed in the main to new construction--DD's, CL's and ACF's [AGF?]; AA training
centers received 17, the Pearl Harbor Pool 22, and Lend-Lease 5.[78]

On June 30, 1945, US Navy combatant and other Navy ships had received 17,365 installations of 40mm guns.[79]

Table I


 Percentage Distribution by Vessel Category


Number of
( ) Represents June 30, 1944
[ ] Represents Dec. 31, 1945
Type of
June 30
Dec. 31
June 30
Quads7641,3081,954(89)  [80]  81(11)  [20]  19
Twins2,4505,3727,574(81)  [46]  40(19)  [54]  60
Singles3,9178,0897,837(5) [80]  81(95)  [92]  93

On December 31, 1944, a total of 4,184 40mm guns had been installed on Navy combatant ships.[80]



Table II

 Percentage Distribution By Type of Ship
(  ) Represents 1943

Number of   Large &     
InstallationsBattle-Carriers HeavyLightDes-DestroyerSub-Minecraft
Jul 1
Dec. 31
Dec. 31
Quads04771,042(45)  28(25)  29(20)  16(9)  10(1)  14(-)   -(-)  -(-)  3
Twins01,3332,486(1)  -(21)  26(1)  1(7)  8(62)  47(8)  16(-)  -(-)  2
Singles0 656    (-)  78(-)  17(-)  - 



Antiaircraft training center and schools, as of July 1, 1945, had received 33 quads, 125 twins, and 47 singles.[81]

Deliveries of 40mm guns to foreign governments under Lend-Lease were not large. At expiration of that program on September 30, 1945, the following deliveries had been made:[82]

United Kingdom44339151
Netherlands2 1
Brazil 815
Russia  260
Mexico  3
Uruguay  1
Greece  1
China  18
Norway  3

In the light of the extensive operations n the Pacific, the losses of 40mm guns from sinkings were unusually small. Wartime losses totaled 24 quads.



220 twins, and 226 singles.

3. Antiaircraft Performance

The continued demands which came from the Fleet for more and more 40mm guns constituted perhaps the best evidence of their value. Specific examples of excellent performance are too abundant and too well known to warrant inclusion in this report. Overall tabulations including such information as plane kills accredited to 40mm guns, ammunition expended, "round per bird" comparisons with other guns, etc., require extremely detailed analysis and explanation to prevent them from being misleading. The available evidence on which to base such tabulations, moreover, is fragmentary. It is felt, therefore, that a more accurate picture can be had from a few accepted generalizations.

There can hardly be any argument with general statements regarding the excellence of the 40mm guns, their effectiveness within range, their ruggedness, their simplicity of operation and maintenance, and the dependence placed upon them by the Fleet for close-in AA defense. While the number of kills



accredited to a specific gun is always a somewhat problematical figure, the number accredited to the 40mm has mounted in rough ratio to the number of guns in action. The picture naturally changed as the tactics of the enemy changed. For example, the emphasis by the Japanese on suicide attacks with planes placed an increasing dependence upon close-in defense by AA guns as opposed to the longer range defense of DP guns. Of the kills made in the period October 1, 1944, to February 1, 1945, in which an attempt was made to assign then to a particular caliber gun, approximately 50% were accredited to 40mm guns.[83] In an earlier period when attacking planes tended to keep at a greater distance, dependence upon DP guns with special ammunition was more marked.

While the 40mm is primarily an AA gun, it should be noted that it has become increasingly effective as a weapon for use against certain types of shore



and surface targets. This is especially true of 40mm guns mounted on submarines and amphibious fire support vessels, action reports late in the war stressed the value of the 40mm gun as an anti-personnel weapon.

4. Maintenance and Performance Problems.

Live round ejection into the case chute, and case chute jams were early difficulties which required correction. A thorough investigation disclosed, that the dropping of live rounds was caused by obstructions in the path of the rammed round which had resulted from an accumulation of tolerances in mass production. A more judicial selection of tolerances and allowances on critical dimensions plus minor changes in profile made it possible to eliminate the failure without resorting to costly hand fitting. Case chute jams were caused primarily by the faulty profile of the deflector, and a redesign of the part eliminated t is difficulty. It was also necessary to make minor changes in design to increase the service life of certain vital parts.[84]



Premature firing of the primer before complete closing of the breech block was encountered. Cases of stand roller path corrosion were common. To eliminate this latter failure, the Naval Gun Factory devised a new method for lubricating the stand and perfected an improved seal to protect the roller bearing assembly from water penetration. Light blows of the firing pin constituted casualties in proof firing, but changes in lubrication eliminated the trouble.

Reports from the Fleet occasionally pointed out that the performance of 40mm guns was sluggish at high angles of elevation. Exhaustive tests proved that with an increase from 0 degrees to 70 degrees the cyclic rate of fire is reduced by approximately 20 rounds per minute. It has been demonstrated, however, that with a wide open setting of the needle valve, a maximum rate of fire at high elevations can be approached.[85]



5. Possibilities with Blind Firing Directors

One of the most interesting commentaries on the history of the Bofors 40mm gun in World War II is the fact that the gun was used during most of the war without benefit of a director which should give it optimum performance - namely, a blind firing director, by early 1943 the design of a lightweight radar equipment had progressed to the point where such equipments could be included in a manually operated director. Thenceforth the inclusion of blind firing features formed a part of all developmental programs for AA directors. Of the early directors produced, however, either weight, maintenance or quantity production problems necessitated discarding or converting the models to other purposes.

The recognizedly urgent Fleet retirement of a light-weight, blind firing AA gun director system became an objective toward which numerous programs were directed. From these efforts, three directors, representing different methods of attack on the same basic problem, were developed. The gun fire control



system, Mark 57, was developed by Section T of the Office of Scientific Research and Development. At the end of August 1945, 251 systems had been produced. Production of the gun fire control system Mark 63, which is basically an incorporation of blind firing features in the Gun Director Mark 51, reached a total of 356 by the end of August 1945. Production for the third system, the Mark 60, which had been developed by the General Electric Company, was can-celled at the end of the war.
Sufficient evidence is not available to permit a complete evaluation of the performance of the 40mm gun in association with these new equipments, but it is unquestionably true that the effectiveness of the 40mm as an AA weapon should be very considerably enhanced through the use of effective blind firing.



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