Why America Put Aircraft Cannons on PT Boats

Why did American PT boats in the Pacific go to sea with a 37mm cannon built for aircraft on their bows? In 1943, after losing destroyers and transports, Japan moved its island garrisons' supplies in shallow coastal barges, and a boat built around torpedoes suddenly faced targets it could not torpedo. This documentary follows the barge war in the Solomon Islands and along the New Guinea coast, from July 1943 into 1944. Machine-gun bullets bounced off armoured Daihatsu barges. The single-shot Army 37mm antitank gun was too slow. The Army Air Forces' automatic M4 37mm aircraft cannon, the gun carried in the nose of the P-39 Airacobra, went onto PT boat bows instead, many of them on mounts made at forward bases. Then Japan answered with armed escort barges, shore batteries and floatplanes, and Lt. Cdr. Robert Kelly reported that sinking a single barge could mean ten minutes at point-blank range. The two Pacific commands built different answers. In the Solomons, where patrol areas were close to base, PT boats stayed torpedo boats with a 37mm and worked alongside slower landing-craft gunboats. In New Guinea, where patrols ran 100 to 150 miles from base, John Harllee's Squadron 12 and Selman Bowling's Squadron 21, the latter with Australian-built guns, put 40mm Bofors on the stern and cut to two torpedoes. Black Cat flying boats, radar and close-inshore patrols made the guns usable, at the price of boats lost on reefs. We also cover the September 1943 Kolombangara evacuation that American destroyers, boats and aircraft failed to stop, captured Japanese documents on the barge losses, Australian Maj. Gen. Frank Berryman's report from the Huon Peninsula, and Gunner's Mate Frank C. Walker of PT-363, awarded the Navy Cross in January 1944. The film follows Robert J. Bulkley's official history. Where it cites the Navy's own records, those are action reports, endorsements and award citations, and figures for barges sunk are the boats' own claims. Captured Japanese documents give the other side's view. We found no wartime record of exactly how the first 37mm aircraft guns reached the boats; later reference books that say they came from crashed fighters cite no document for it. Sources: Robert J. Bulkley Jr., At Close Quarters: PT Boats in the United States Navy (Naval History Division, 1962) — https://www.ibiblio.org/hyperwar/USN/... Samuel Eliot Morison, History of U.S. Naval Operations in World War II, vol. VI: Breaking the Bismarcks Barrier (1950) — https://archive.org/details/husno-vol... Office of the Chief of Ordnance, Catalog of Standard Ordnance Items, vol. II (1944) — https://archive.org/details/CatalogOf... War Department, TM-E 30-480 Handbook on Japanese Military Forces (1944) Naval History and Heritage Command, "U.S. Navy PT Boats" — https://www.history.navy.mil/research... NHHC photograph NH 96501, 37mm automatic cannon (aircraft type) on a PT boat bow U.S. Strategic Bombing Survey, Interrogations of Japanese Officials (1946) If someone in your family served on a PT boat, built one, or crewed its guns, tell us the boat number and squadron in the comments. #PTBoat #WWII #PacificWar