The 90mm Anti-Aircraft Artillery was a high-velocity replacement for the 3-inch M1918 gun, the standard before World War II. The 1939-1940 German Blitzkrieg made clear to all military planners the need for improved air defenses. In 1940 the T2 90mm design was standardized as the 90mm Gun M3. It was called the M1 90mm AAA Gun, Towed when mated with its mount and carriage. The carriage rode on four road wheels and had huge folding outriggers to steady the gun when it was fired.
Almost immediately, improvements were made and the revised weapon was redesignated M1A1 90mm Towed Anti-Aircraft Gun, standardized in May 1941. The M1A1 was towed on its single axle, dual-wheel carriage with a distinctive perforated firing platform. The M1A1 90mm went into mass production with tens of thousands of these mobile guns produced during World War II.
Feedback of combat lessons resulted in another upgrade in May 1943 when the M2 variant was introduced. The main changes were a new mount that could be depressed below horizontal (for use against tanks and fortifications in addition to its anti-aircraft role), an electric rammer, a shield to protect the crew, and a fire control computer.
Typically, each 90mm AAA Gun Battallion consisted of a Headquarters and HQ Battery, and four firing Batteries, A to D. Each firing battery had four towed 90mm guns plus fire direction equipment. After the electronic and mounting upgrades during World War II, this would consist of the M2 90mm Anti-Aircraft gun, the SCR-584 microwave tracking radar in a trailer, the M-9 or M-10 gun director system in a second trailer, and supporting equipment such as generators.
The 90mm AAA had an altitude capability of 30,000 feet and a range of 14 miles, firing a 24 pound shell. The ammunition was improved dramatically when fitted with VT proximity fuses at the end of 1944. The 90mm gun was very effective and was credited with downing many enemy aircraft during World War II. When controlled by the SCR-584 radar set, the U.S. 90mm was the finest anti-aircraft gun of World War Two. A single 90mm gun could put 20 to 28 rounds in the air every minute -- a battery of four guns was devestating when on a single target. A crew of 8 to 10 was required to operate and maintain the 90mm gun, including the section chief, loader, gunner, azimuth pointer, elevation pointer and an ammo section.
While originally intended for use against airborne targets, the 90mm gun was often brought to bear on ground fortifications, troop concentrations, or armored vehicles. In the Pacific Theater, the M1A1 became the standard antiaircraft artillery for the defense and AAA battalions of the Marine Corps. The Marine Corps' 90mms generally landed early in an amphibious assault to provide immediate AAA defense at the beachhead as well as an offensive role directed against ground targets.
90mm Anti-Aircraft Artillery at Antwerp, Belgium
During the 1944-1945 German bombing campaign against the Allies in the Belgian port of Antwerp, 90mm AAA operated 22 hours a day with two hours a day for maintenance. The life expectancy of the gun tube was 1,500 to 2,000 rounds and many batteries wore out three or four sets of tubes over the course of the campaign. After the third wore out, the gun slide had to be replaced as well. Due to shortages of replacements some barrels were retained until they fired as many as 2,500 rounds but this was a dangerous practice. When the tube became that worn, muzzle velocity grew erratic and, in some cases, the lands in the tube began to peel. For much of the four months of December 1944 to March 1945, nearly every 90mm anti-aircraft gun barrel produced was sent to Antwerp, while units in the Pacific and Mediterranean had to wait. In February ammunition ran low despite emergency deliveries by air. The M-13 fuze-setter and the hydraulic rammer were considered problems. In the case of the latter many gun crews resorted to ramming by hand, a practice many a section chief maintained was better than hydraulic ramming anyway.
90mm Anti-Aircraft Artillery After World War II
After World War II, 90mm anti-aircraft artillery saw combat service in Korea. Peak deployment of the 90mm gun for U.S. continental defense occurred in 1953, when 42 battalions were on line, each battalion having four batteries, and each battery having four guns. These 672 guns ringed cities and essential defense and industrial sites to protect the United States. The role of the 90mm anti-aircraft artillery ended with the advent of missiles for air defense, beginning with the Nike Ajax in the mid-1950s.
Specifications of the 90mm Anti-Aircraft Gun (M1A1)
15 ft, 6 in.
13 ft, 8 in.
Vertical to -5°
Other Uses of the 90mm Anti-Aircraft Gun
The 90mm Anti-Aircraft Gun was highly successful and was therefore adapted to other uses. As an anti-tank gun it was the main armament for the M-36 Tank Destroyer that used the chassis of the M-4A3 Sherman tank with an M3 90mm gun in an M4 mount in the turret. On a fixed mount M3, in an armored turret, it was used for coast defense with nomenclature Anti-Motor Torpedo Boat (AMTB).
Manuals for the 90mm Anti-Aircraft Gun
SOP 90 mm Gun M1, on Mount M3 (Coast Artillery)
SOP 90mm AA Gun on M1A1 Mount
SOP 90mm AA Gun M2, on Mount M2
90mm Gun M1 and M1A1
90mm Gun M2 and Antiaircraft Mount M2
90mm Gun M1 and Mount M3
90mm Gun M1 and Mounts M1 and M1A1 Gun and Upper Carriage
90mm Gun M1 and Mounts M1 and M1A1 Lower Carriage
90mm Gun M3 Mounted in Combat Vehicles (Mount M4)
African-American USMC 51st Composite Defense Battalion training on the 90mm anti-aircraft gun at Montford Point, Camp Lejeune, New River, NC, 1942.
A 90mm anti-aircraft gun on Omaha Beach shortly after the invasion, 6 June 1944.
90mm anti-aircraft artillery gun emplacement. No. 4 gun, D Battery, 98th AAA Gun Battalion, 137th AAA Group Okinawa, 18 July 1945.
M2 90mm anti-aircraft guns used as Division Artillery for 1st ROK Division fire against the North Korean forces north of Taegu, 15 September 1950.