The Swedish-designed rapid-fire Bofors 40-mm gun was the most widely used antiaircraft weapon of World War II. In the 1939–45 conflict, the Bofors was in the arsenal of most Allied and Axis nations and in all theaters of the war. The U.S. Army had a large number of them, and they were the U.S. Navy’s most widely used shipboard gun. The weapon was reliable, efficient, and highly effective, and it could be mounted on virtually anything that floated.
The Bofors 40-mm was first produced in 1930 and initially was delivered to the Swedish Navy in 1932. Foreign orders came quickly, and by the outbreak of war in Europe in 1939, 18 nations were using it, with licensed production in several of them. Beyond countries that bought and produced the guns, hundreds were captured by Germany from British and Dutch forces in 1940, while Japan obtained Bofors when it conquered the Dutch East Indies in 1942.
By 1940, the U.S. Navy had become aware of the weapon’s reportedly remarkable effectiveness but struggled with how to obtain samples for evaluation. Europe was wrapped in conflict, with German forces largely isolating Sweden by their campaigns in Denmark and Norway.
The answer came in the converted passenger liner American Legion. She departed New York City in February 1940 on her maiden voyage as a military transport, bound for Panama. During the next few months, the ship made five round-trip voyages to the Panama Canal Zone carrying civilian and military passengers. The worsening situation in Europe led to the ship being given a special mission.
Soon thereafter, President Franklin D. Roosevelt personally directed that the American Legion sail from New York as soon as possible for Petsamo, Finland. At the time, Finland was officially neutral, although friendly to Nazi Germany and engaged in planning for renewal of conflict against the Soviet Union.
At Petsamo, the American Legion was to embark Crown Princess Martha of Norway and her party to bring them to the United States, Norway having been seized by Germany the previous spring. The President also desired that Florence Jaffray Harriman, the former U.S. minister to Norway, return in the ship along with other U.S. citizens trying to leave Scandinavian countries.
The American Legion sailed for Finland on 25 July 1940, with her neutrality shown clearly by the U.S. flags painted prominently on her off-white sides. She reached Petsamo on 6 August, and on the 15th, she embarked Crown Princess Martha and her three children. The Army-operated troopship also embarked numerous U.S. nationals as well as refugees from Finland, Estonia, Latvia, Lithuania, Sweden, Norway, Denmark, Germany, and the Netherlands—897 passengers in all. (Among them was a young Danish comedian and musician named Victor Borge, soon to become an American entertainment icon.)
Unbeknownst to all but a handful of individuals in the ship, the American Legion also took on board an important cargo during her stay at Petsamo. After a Herculean effort that involved taking the special cargo by truck the entire length of Sweden, the ship loaded a twin-mount 40-mm Bofors antiaircraft gun, spare parts, and 3,000 rounds of ammunition.
The U.S. State Department had obtained the cooperation of three governments to make possible the shipment of the Bofors gun—British, Swedish, and Finnish. The move came none too soon, for the American Legion was the last neutral ship to depart Petsamo.
The vessel reached New York without incident after an Atlantic crossing of 12 days, escorted for the final leg by several U.S. destroyers. The transport unloaded the Bofors at New York, from where it was immediately shipped to a Navy test facility at Dahlgren, Virginia. The tests were successful, and the gun quickly was copied and placed in production. Its installation in U.S. warships began in mid-1942.
The U.S. Navy procured the gun in single, twin, and quad mounts, installing them on ships ranging in size from battleships and aircraft carriers to PT boats. By the end of the war the standard armament of an Iowa-class battleship included 80 of the 40-mm guns, while Essex-class carriers normally had 72. At one point, the venerable carrier Saratoga (CV-3) had 100 40-mm guns. Destroyers and destroyer escorts had several 40-mm mounts, as did lesser warships, landing ships, and auxiliaries. Many U.S. submarines had one or two single “wet mount” 40-mm guns on deck.
In the United States, the Army initially had little interest in the Bofors because of the domestic 37-mm gun M1. However, the Bofors was lighter than the M1, fired a heavier shell, and used ammunition in common with British guns, leading to its eventual adoption by the U.S. Army. By war’s end, the Army had thousands of single-barrel 40-mm Bofors, usually on four-wheel towed carriages. During amphibious landings, soldiers would sometimes set them up on landing ships to add their fire to shipboard batteries, and in coastal operations, the British used barges fitted with a pair of antiaircraft Bofors 40-mm guns for protection of the landing area (calling these craft landing barges, flak, or LBFs).
U.S. Army versions had a cyclic rate of fire of 120 rounds per minute—160 for naval guns; however, because the weapon was manually loaded, an effective rate of 60 to 90 rounds per minute was more realistic. The weapon ordinarily was manned by two gunners and several loaders, plus either a radio talker or pointer to designate approaching aircraft to the gunner. Ammunition was loaded in four-round clips. The Army gun had a simple open sight, while some naval guns had radar directors.
Weights of the gun mounts varied. The single gun on a towed carriage weighed some 5,500 pounds. The Army guns were air-cooled; the naval twin-barrel and quad weapons had water cooling jackets. The armor-piercing 40-mm round—the gun’s heaviest projectile—weighed two pounds. Maximum altitude at a 90-degree elevation was 7,600 yards, while maximum horizontal range—at 42 degrees elevation—was 11,000 yards.
During World War II, the gun was produced in the United States, primarily by Chrysler and the Naval Gun Factory in Washington, D.C. The York Safe and Lock Co. began production but suffered numerous problems in the effort.
The Bofors 40-mm gun still can be found in several navies today, albeit not on board U.S. Navy ships.
The Ship that Brought the Bofors
The passenger liner American Legion was built in 1919–21 by the New York Shipbuilding Corp. in Camden, New Jersey. After being held by the government for four years, the ship entered commercial service between the world wars. She was reacquired by the War Department in November 1939 for use as a troop transport and underwent modification for her new role. Her original name was retained.
Following her historic political-military voyage of 1940, the American Legion sailed as a troop transport, carrying soldiers and Marines far and wide. She was transferred from the War Department (Army) to the Navy in August 1941 and designated as a transport, AP-35. Repainted gray and manned by sailors, she operated in the Caribbean and then the Pacific, participating in the invasions of Guadalcanal in August 1942 and Bougainville in the Solomon Islands in November 1943. In between, on 1 February 1943, she was reclassified as an attack transport—APA-17—as she was fitted to carry landing craft and assault equipment for embarked troops.
The American Legion served in the Pacific to the end of World War II. Finally, she was decommissioned and stricken from the Navy List at Olympia, Washington, on 28 March 1946. She was placed in the reserve fleet, but in early 1948 she was sold for scrap.