the T139 and standardized as the 90 mm gun M41, equipped the M48 Patton tanks used in the Vietnam War. The M41 with a modified recoil system was mounted as the 90 mm gun M54 on the M56 Scorpion anti-tank vehicle. Coast artillery During World War II the Coast Artillery Corps adopted the 90 mm M1 to supplement or replace aging three-inch guns in harbor defense commands in CONUS and US territories. The guns were organized in anti-motor torpedo boat (AMTB) batteries, typically with four 90 mm guns and two 37 mm or 40 mm AA guns each. Typically two of the 90 mm guns were on T3/M3 fixed mounts and two were on towed M1A1 or M2 mounts, with the 37 mm or 40 mm weapons on single towed mounts. The T3/M3 mount was designed for anti-surface or anti-aircraft fire. Emplacements for at least 90 batteries of two fixed guns each, plus mobile weapons, were constructed in CONUS, Panama, Alaska, Hawaii, Puerto Rico, and elsewhere in 1943. Variants M1 Towed anti-aircraft gun. Approved for service in 1940. Fixed on T3/M3 mount for coastal artillery service M1A1 Towed anti-aircraft gun. Production began in 1940. It featured the M8A1 spring rammer. Its rate of fire was 20 rounds per minute. M2 A complete redesign to make the gun dual role, functioning as an anti-tank gun as well as an anti-aircraft gun. The ammunition feed was upgraded and an automatic fuze setter-rammer, the M20, was added. This enabled the rate of fire to reach up to 24 rounds per minute. Elevation was improved with the gun able to depress to −10 degrees. To protect the crew, a large metal shield was added. The M2 was the standard weapon by May 13, 1943. From the march it could fire from its wheels in three minutes, and from a fully emplaced position in seven minutes. In 1944 the weapon was enhanced with the addition of proximity fused shells. M3 A tank-anti-tank version of the gun. It was used to equip the M36 tank destroyer and the M26 Pershing tank. It is also known as the 90 mm L/53. M3A1 M3 gun with single baffle muzzle brake and bore evacuator, used on M46 Patton and early versions of the M48 Patton tanks and refurbished M36 tank destroyers during the Korean War. M3 ammunition M71 HE – (projectile) M77 AP – (projectile) M82 APC – (projectile)