Chrysler, Gun Maker: Bofors Guns of World War II

Navy Bofors anti-aircraft guns

Bofors to the rescue: Before the Bofors and Oerlikon guns, there were no effective long-range anti-aircraft weapons between five-inch batteries and pom-poms. The Bofors had a good range, were small and cheap compared with the five-inch batteries, and sent out nearly continuous, yet accurate, fire. The pom-poms were less accurate at long range, though effective at short range; their ancestory was in belt-fed machine guns, and they sent out two shots in quick succession (pom-pom) before pausing while the Bofors was continuous. The Oerlikon had a shorter range and was a 20mm gun.

Rear Admiral W.H.P. Blandy, Chief of the Bureau of Ordnance, wrote in July 1943: “The exceptional performance of the 40-mm anti-aircraft gun which has already earned high praise in all theatres of war was strongly echoed in a combat report from the captain of a converted carrier ... ‘They can reach out for enemy planes before they come in too close. It’s a beautiful gun, the best I've seen.’ You of Chrysler in producing these outstanding guns for the Navy are helping to safeguard our ships’ crews and cargoes at sea. You can make no greater contribution to the war effort than to do your best to turn them out.” 

The Bofors guns were, due to accuracy, reliability, and range, far better than any other anti-aircraft weapons of the time. Designed to fire 120 shells per minute (two explosive shells per second), it was primarily defensive in nature, used against attacking aircraft. Its makers, in Sweden, simply could not build enough for the U.S. Army and Navy.

Chrysler Corporation signed up to build huge numbers of the complex guns at a fraction of the cost the Swedish inventors needed; the company could have lost a great deal of money had they failed. At the time, they simply were not seen as a candidate for mass production.

K.T. Keller might have assumed that Chrysler Engineering could do it by simplifying the design, but in the end, it turned out that every piece and part of the gun appeared to have a function and a purpose. The design could not be simplified. Yet, Chrysler produced 60,000 guns and more than 120,000 barrels, for half the original cost, and taking less than half the original production time. The Army’s needs were filled as early as 1943. The Navy kept production going, with their need to outfit ships as they were built and add installations to existing ships.

Army Bofors guns

The Navy used the 40mm gun to cover landing operations; it was fired against armaments protected by pillboxes or natural barriers; and it was the primary weapon used by PT boats against lesser ships and airplanes, with a range of around 7,500 feet.

The gun contained over a thousand parts, and the rifle had an accelerated spiral to spin the shell to an amazing 19,000 rpm at the muzzle. The rounds were shot out at 2,700 feet per second, 120 rounds per minute (later, Chrysler raised their capacity to 140 rounds per minute).

Building the Bofors guns at Chrysler Corporation: challenges and accomplishments

The first order came in 1938, when the Army asked Chrysler to make a small number of anti-aircraft shells, so they would know how to mass produce them if needed. Chrysler Corporation asked about making the actual guns, and the Army turned over its blueprints for the 37 mm Browning gun. Chrysler made a cost estimate, but no action followed until the Army asked Chrysler to make some 75 mm shells, for the same reason. In December 1940, General Knudsen asked K.T. Keller to make the 37 mm guns after all, but on December 31, the Army dropped plans to use the Brownings and instead joined the Navy in adopting the Bofors. The Navy had, under chief of ordnance Admiral W.H.P. Blandy, chosen to adopt the Bofors guns (and smaller, Swiss Oerlikons), and had arranged to get the drawings for the Swedish gun from the British.

making the breech blocks

The Bofors presented some challenges, since the drawings were done in Swedish, using metric units, and read from the first angle of projection (American practice used the third angle); the blueprints also read “backwards” from American practice, and was much less precise than needed (the European practice of the time was to fix small discrepancies by hand, in assembly). Chrysler engineers had to revise the blueprints to American standards, and fix them to absolute dimensions; for the Navy, in addition, Chrysler had to convert it into a twin-barrel design with water cooling and other modifications.

It later turned out that regardless of translation, the guns were not made exactly to specifications in Sweden; the actual guns were apparently altered at assembly time in order to work, by their craftsmen. Thus, Chrysler may have ended up measuring the actual weapons, as manufactured, in some cases.

Originally, the York Safe and Lock Company was the prime contractor; York subcontracted most of its work. As time went on, Chrysler was given more responsibility for production and York was “gradually relieved” of its key functions.

Other domestic companies also built the guns, Chrysler was responsible for adapting them to mass production. Buying the rights to build the guns and ammunition from Bofors cost $600,000 in June 1941 — $100,000 of which, being continent on the loan of two engineers, was never paid.

bofors guns

Engineers trying to study the workings of the gun found it to be extremely complex, and while they tried to take high speed movies of the weapon in action, no camera was capable of the needed speeds until near the end of the war. They were not able to simplify the design, but they were able to make them more quickly.

No fewer than 12 Chrysler factories were involved in making and assembling the parts, and in the end, the project involved 2,000 subcontractors in 330 cities. The guns required 3,000 machines for creation, with 10,000 employees, 1 million square feet of floor space, and 2,000 subcontractors.

Chrysler claimed that it took assembly time for each gun down from 450 hours (in Sweden, by Bofors itself) to just ten man-hours, saving 1.3 million man-hours of labor during 1943 alone. (It is hard to tell whether this is a fair comparison; whether this was the total time to build each gun, including all subcontractors’ work, is unclear, and it is possible the number represents final assembly alone. The use of sintered metal certainly slashed component machining time.)

Part of the credit for increased parts interchangeability goes to H.A. Matson, a civilian engineer attached to the military, who coordinated the Army, Navy, and British drawings so that all three would use identical sub-assemblies, interchangeably. That meant that Australian parts would fit in American guns. It appears that the guns actually made by Bofors, since so much work was done by hand, might not have had the same level of parts interchangeability even within the same type of unit.

gun barrels

The Swedes machined nearly every large part from blocks of metal; but Chrysler Engineering used a casting, forging, or stamping wherever possible, cutting around a third (around 150 hours) of the labor time out. Chrysler used its Amplex division for powdered metal parts to save 65,589 man-hours in 1943, by changing nine parts from castings to powdered metal.

The production team worked on assembly and machining issues, garnering the rest of the savings. Few of them had production experience with guns, though H.R. Matheny had made gun barrels in World War I.

Redesigning ten items ended up saving 7.5 million pounds of material and 1.9 million man-hours in a single year while eliminating the need for 30 machines.

Chrysler’s parts were often made with greater precision by unskilled labor than they had been by highly skilled Swedish craftsmen.

gun breech ringsDue to the complex countours, machining, and blending needs, inspection was intense, with the breech ring alone passing 625 inspection gauges, each set 20% tougher than the print tolerances; Navy inspectors enforced 100% inspections (no sampling). Machinists had to shut down their machines if a single part failed a single test, until the problem was found. Even roughing cuts were tested, and machine tools could have 17 gauges. Assemblies and incoming metals were tested as well (with metallurgists testing the alloys).

The largest, most intricate part was made from a solid 300 pound forging; by the time it was finished it weighed just 105 pounds. One part required 130 different machining operations. The “heart” of the weapon, the breech lock, breech ring, and recoil assembly was made in the Jefferson-Kercheval arsenal; most of the rest of the Bofors was made in Highland Park and Plymouth.

Scrap rates started out high, and came down to less than 2% — lower than in ordinary manufacturing of the time. Indeed, according to a 1943 report, the percentage of scrap in the gun barrel plant was lower than any other similar plant in the world.

In 1942, the Army increased its order from 300 to 1,500 guns a month, with twice as many barrels as guns (for spares), and the goal was passed in November. In December, Chrysler managed to build 1,600 for the Army and 135 for the Navy. At that point, the Army cut their order, their needs for the war fulfilled — largely because they now assumed they would not need defensive anti-aircraft guns in North America. The Navy still needed Bofors guns for every ship, and naval production was still in full swing.

By the end of 1943, Chrysler had sent 28,892 guns to both Army and Navy; for 1943 itself, the total cost was $46 million. In August 1943, Chrysler said it was making 4½ times the number of guns originally scheduled.

Bofors antiaircraft guns in action

The first Bofors weapons were placed on the Midway ships as they were putting to sea, and played a substantial role in the first major defeat of the Japanese Navy. One ship shot down 32 enemy planes in 30 minutes with the new guns — which had not yet been test-fired. Each of the new guns threw 20 times the weight of steel into the air as the old ones. The weapons destroyed the effectiveness of kamikaze attacks, tearing many incoming attack planes apart before they could hit.

making Bofors antiaircraft guns

One problem with the early Bofors guns was the extractor arm, which ejects empty shells; they were designed to last 1,500 rounds. Engineers had to increase the durability, without changing the size; engineers in the Chrysler stress lab found that removing a small amount of material tripled its lifespan, by making it more flexible.

The company also made gun-sights, building at least a thousand of them before the Navy sent out an order, starting out with 25 sets per day and escalating to 100 per day. Drives for the guns were made by a variety of companies, including Ford, which could not keep up with Chrysler’s production levels.

The Navy appears to have appreciated the new weapons, actually telegraphing Chrysler Corporation with the creations’ serial numbers when their guns shot down enemy planes. The Bofors were all the more effective for being hooked up to radar units, providing radar-guided fire. Admiral A.C. Davis, who commanded an aircraft carrier, wired, “It is not possible to tell you how gratifying it was to see the really wonderful control and performance of the entire installation.” They also proved devastatingly effective in eliminating ground cover, including caves, when American troops were engaged in taking islands through the Pacific on their way to Japan.

building guns

A press release from early 1944 noted that Chrysler-built 40 mm anti-aircraft guns mounted on one battleship knocked out 32 Japanese plans in the South Pacific, in a single battle. Captain Thomas Gatch, skipper of the ship, called Japanese torpedo bombers “duck soup” for the guns, which knocked out more than one plane per minute in the battle; his ship was a new design, specifically equipped to fight aircraft in carrier task-force screens. The concentrated air attack was similar to earlier ones which had destroyed the British capital ships Repulse and Prince of Wales. (On the same night, afterwards, the same ship sank four Japanese military vessels; weeks later, the ship sank three or four Japanese cruisers in the battle of Guadalcanal.) Making this more impressive, the ship was manned largely by reservists and inexperienced men; even mess attendants, at their own request, manned the guns.

Primary Sources: Mobilized, by Wesley Stout, 1949; added materials sent to Gene Yetter by Chrysler Historical

bofors guns

Want to learn more? See Allpar’s “Chrysler and the Military” page.

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