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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 were small and cheap compared with the big batteries, and sent out nearly continuous, yet accurate, fire. Pom-poms were less accurate at long range, though effective at short range; based on belt-fed machine guns, they sent out two shots and paused (pom-pom), while the Bofors was continuous. The 20mm Oerlikon had a shorter range.

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.” 

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

Chrysler signed up to build the complex guns at a fraction of the cost the Swedes needed; and could have lost a great deal of money had they failed. Bofors guns were not seen by most people as a candidate for mass production.

K.T. Keller might have assumed that Chrysler Engineering could do it by simplifying the design, but every piece and part of the gun appeared to have a purpose. Still, Chrysler produced 60,000 guns and more than 120,000 barrels, for half the original cost and less than half of the original production time. The Army’s needs were filled by 1943, while the Navy kept outfitting new ships and adding guns to existing ships.

Army Bofors guns

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).

The Navy also used the 40mm gun to cover landings, firing against pillboxes or natural barriers, using it as the PT boats’ primary weapon against airplanes and lesser ships, with a range of around 7,500 feet.

Building the Bofors guns at Chrysler Corporation: challenges and accomplishments

In 1938, the Army asked Chrysler to make a small number of anti-aircraft shells, so they would know how to mass produce them if needed. When engineers asked about making the actual guns, 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 switched to the Bofors, as the Army had before it. The Navy had already arranged to get the drawings for the Swedish gun from the British, paying Bofors $500,000 in 1941 (another $100,000, continent on the loan of two engineers, was never paid).

making the breech blocks

The drawings were in Swedish, using metric units, and read from the first angle of projection (American practice used the third angle); the blueprints 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). Chrysler engineers had to revise the blueprints and fix them to absolute dimensions; for the Navy, they also had to convert it into a twin-barrel design with water cooling and other modifications.

It later turned out that the guns were not made exactly to specifications anyway; they were altered at assembly time by craftsmen. Thus, Chrysler probably ended up taking apart and measuring the actual weapons after they were built, reverse engineering the final product.

The York Safe and Lock Company was to be the prime contractor, but York subcontracted most of its work, and as Chrysler was given more responsibility for production, York was “gradually relieved” of its key functions. While other American companies built the guns, Chrysler was responsible for adapting them to mass production.

bofors guns

Engineers found the gun to be extremely complex, and while they tried to take high speed movies of the weapon in action, no camera was fast enough 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, and the project eventually involved 3,000 machines, 10,000 employees, one million square feet of floor space, and 2,000 subcontractors in 330 cities.

H.A. Matson, a civilian engineer attached to the military, coordinated the Army, Navy, and British drawings so that all three would use identical sub-assemblies, and, for example, Australian parts would fit in American guns.

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.

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, or final assembly alone, is unknown.)

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. In the end, 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; every single unit was inspected. Machinists had to shut down their machines if a single part failed a 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 ended up being 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, and the Army cut their order, their needs for the war fulfilled. 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. 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, and was originally designed to last 1,500 rounds. Engineers had to increase the durability; 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, at the rate of 100 sets per day by the end. Drives were made by a variety of companies, including Ford, which could not keep up with Chrysler’s production levels.

The Navy telegraphed Chrysler Corporation with their 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 reported 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 wrote that the weapons knocked out more than one plane per minute in the battle (his ship was a new design, created to fight aircraft in carrier task-force screens). The concentrated air attack was similar to those 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 at least three 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

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