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NavSource Online: Battleship Photo Archive

Quadruple 40mm Mount

Click On Image For Full Size Image	Size	Image Description		Contributed By And/Or Copyright
	141k	Photo taken in the Spring of 1945 showing the crowded condition of the extra 40mm and 20mm guns. They were added wherever deck space was available. The quadruple 40mm Mount was developed as a replacement for the 1.1in to counter the increasing air threat. The Bofors used the energy of its recoil to operate its breech and its feed. The prominent spring surrounding the barrel forward of the breech mechanism was a characteristic feature of the weapon. The trigger controlled only the rammer; once ramming began, loading and firing were automatic. Much of the Bofors enormous popularity could be traced to the much greater power of its ammunition compared to that of the 1.1in. Muzzle velocity rose to 2890ft/sec and the standard tracer round burned for 8.5-10.5 seconds (4200-4500yds). It fired armor-piercing, high explosive and incendiary rounds with a projectile weight just under 2lb, more than twice that of the 1.1in. No VT fuze was available for this weapon during the war. The rate of fire per barrel slightly exeeded that of the 1.1in. The Bofors as said before, was liked for its high power, its ruggedness and its simplicity of operation and maintenance. The percentage of aircraft kills attributed to it grew as the Japanese came to rely more heavily on suicide attacks late in WWII. Between 1 October 1944 and 1 February 1945 about half of all aircraft shot down by US surface ships were credited to the Bofors . In the extensive kamikaze rearmament program of 1945 in which many Fleet destroyers were fitted with additional Bofors guns at the expense of their torpedo tubes, the same sort of popularity shows. Only at the very end of WWII it became clear that a replacement was needed as the Bofors was not able to destroy an approaching kamikaze soon enough to keep it from hitting. Firing a much heavier shell, the 3in/50 could put up more metal than could the Twin 40mm and more effectively, since it would fire VT-fuzed shells. Ammunition for the Bofors was loaded in the form of four-round clips atop the breech mechanism, each full fixed round weighing about 4.8lb, for a total of about 19. The Bofors feed atop the gun could hold two clips, so that fire could be maintained continuously passing clip after clip into the gun. The first series of quadruple 40mm mounts were allocated to the South Dakota Class (BB-57-60) battleships, which received six MK.2. The Mk.4 was a lightweight quadruple mount developed by Northern Ordnance, in which about 1000lb was saved by the use of a GE drive, and an additional 2500lb of electrical equipment, including amplidyne motors, was stowed below decks. About 100 had been made by VJ-Day. It weighed 25,140lb, elevated/trained at 55 degrees per second and its introduction shows the needs of the Fleet of 1945. It had elevation limits of +90-/-15 degrees. Although meant to be replaced in 1945, by the 3in/50, it remained through the 1970's for lack of funding. Eventually a VT-fuze was developed for it but there seemed to be no interst in new 40mm development.		U.S. Navy Photograph & text submitted by Pieter Bakels. Photo added 12/09/07.

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