Twin 3"/50 Anti-Aircraft Gun

In 1944-1945, the USN found that their 20 mm Oerlikons and 40 mm Bofors batteries were ineffective in stopping Japanese Kamikaze attacks. Only the 5โ€œ/38 (12.7 cm) fired a round large enough to destroy a determined attacker and this weapon was too heavy to use in the numbers necessary. This problem led to an accelerated program to develop an intermediate-caliber weapon that could fire a VT fuzed shell.

The weapon chosen was the standard 3โ€/50 (7.62 cm) Mark 22 used on many Destroyer Escorts and auxiliaries built during the latter part of World War II. This was the smallest-caliber weapon which could still use the VT fuzes available at the time. It also had a concentric counter-recoil spring, which meant that it was more easily adapted for automatic fire, which was achieved with an electrically driven auto-loader using revolving sprockets. BuOrd rushed this through the design phase, with the first prototype being ready for test firing on 1 September 1945.

Although completed too late for service during World War II, this weapon was widely used on many USA ships from the late 1940s through to the 1980s.

Dimensionally, the new twin 3โ€œ/50 (7.62 cm) mounting was the same size as the quad 40 mm Bofors mounting, although it weighed a bit more. The additional weight meant that these guns replaced the Bofors guns on a one for three basis, rather than the originally intended one for two basis. Ammunition was loaded from each side into the auto-loader. The sprockets turned intermittently, transporting the rounds to a loading tray, which swung down to be in line with the breech where a rammer then catapulted the rounds directly into the firing-chamber, with the breech-closing mechanism being triggered by the edge of the cartridge case as it tripped one of the ejectors. Effectively, the auto-loader simply replaced the crewmen whose job it was to push shells into the breech. The auto-loader is synchronized with the rhythm of the recoil motion, so that new rounds are ready to be rammed at the instant that the previous cartridge is ejected. Ballistically, the new automatic weapon had the same characteristics as the older weapon, although the higher rate of fire did result in a shorter barrel life.