90 mm Gun M1/M2/M3

The American 90 mm gun served as a primary heavy anti-aircraft and anti-tank gun, playing a role similar to the renowned German 88 mm gun. It was the US's primary anti-aircraft gun from just prior to the opening of World War II into the 1950s, when most anti-aircraft artillery was replaced by guided missile systems. As a tank gun, it was the main weapon of the M36 tank destroyer and M26 Pershing tank, as well as a number of post-war tanks.

History
Prior to World War II, the primary US anti-aircraft gun was the 3-inch M1918 gun (76.2 mm L/50), a widely-used caliber for this class of weapon. Similar weapons were in British, Soviet and other arsenals. There had been several upgrades to the weapon over its history, including the experimental T8 and T9 versions developed in the early 1930s that were intended to enter service later in the decade. However the US Army became interested in a much more capable weapon instead, and on June 9, 1938 it issued a development contract calling for two new guns, one of 90 mm which it felt was the largest possible size that was still capable of being manually loaded at high elevations, and another, using assisted loading, of 120 mm caliber. The new design seemed so much better than developments of the older 3-inch that work on the 3-inch T9 was canceled in 1938 just as it became production-ready. By 1940 the second development of the 90 mm design, the T2, was standardized as the 90 mm M1, while its larger cousin became the 120 mm M1 gun.

A few hundred M1s were completed when several improvements were added to produce the 90 mm M1A1, which entered production in late 1940 and was accepted as the standard on May 22, 1941. The M1A1 included an improved mount and spring-rammer on the breech, with the result that firing rates went up to 20 rounds per minute. Several thousand were available when the US entered the war, and the M1A1 was their standard anti-aircraft gun for the rest of the conflict. Production rates continued to improve, topping out in the low thousands per month.

Like the German 88, and the British QF 3.7 inch AA gun, the M1A1 found itself facing tanks in combat, but unlike the others it could not be depressed to fire against them. On September 11, 1942 the Army issued specifications for a new mount to allow it to be used in this role, which resulted in the 90 mm M2, introducing yet another new mount that could be depressed to 10 degrees below the horizontal and featured a new electrically-assisted rammer. It became the standard weapon from May 13, 1943.

Anti-aircraft operation
In anti-aircraft use the guns were normally operated in groups of four, controlled by the M7 or M9 Director or Kerrison Predictors. Radar direction was common, starting with the SCR-268 in 1941, which was not accurate enough to directly lay the guns, but provided accurate ranging throughout the engagement. For night-time use, a searchlight was slaved to the radar with a beam width set so that the target would be somewhere in the beam when it was turned on, at which point the engagement continued as in the day. In 1944 the system was dramatically upgraded with the addition of the SCR-584 microwave radar, which was accurate to about 0.06 degrees (1 mil) and provided automatic tracking as well. With the SCR-584, direction and range information was sent directly to the Bell Labs M3 Gun Data Computer, and M9 Director, which could direct and lay the guns automatically. All the crews had to do was load the guns. With the SCR-584 the 90 mm became arguably the best anti-aircraft weapon of the war.



Anti-tank developments
The M3 was also adapted as the main gun for various armored vehicles, starting with the experimental T7 which was accepted as the 90 mm M3. The test firing of the M3 took place on an M10 tank destroyer in early 1943. The gun was used on the M36 tank destroyer, and the M26 Pershing tank.

A number of experimental versions were developed on the basic M3 pattern, including the T14 which included a standard muzzle brake, the T15 series with an improved muzzle velocity of about 975 m per second, the even higher velocity T18 and the T19, which was an attempt to reduce barrel wear. The T21, which was intended for wheeled vehicles, and the T22, which used the breech from the standard 105 mm M2 howitzer to take larger charge cartridges. None of these versions entered service.

In the post-war era development of the T15 continued as the T54, which included the ability to fire tungsten-cored shells at much higher velocities. The T54 was the main armament of the M47 and M48 Patton tanks, and the M56 Scorpion anti-tank vehicle.

M1

 * Towed anti-aircraft gun. Approved for service in 1940.
 * Fixed on M3 mount for Coast Artillery

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 &minus;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
An 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.

Surviving examples

 * One AAA at NTC, Fort Irwin, CA post museum.
 * One AAA at CFB Borden, Ontario, Canada
 * One AAA at Sangudo Alberta
 * One AAA at Whycocomagh, Nova Scotia
 * One AAA at RCHA Museum, CFB Shilo, Manitoba, Canada
 * One AAA at Shilo Manitoba, Canada (private collector)
 * One AAA at Lembourg, Saskatchewan, Canada (private collector)
 * One AAA at Fort Rodd Hill - Colwood, BC
 * One at Savannah, Georgia: National Guard Fairgrounds
 * One at Arundel, Quebec, Canada: Legion Hall
 * One AAA at Sault Ste Marie Ontario
 * One on barbette carriage at Shemya, Alaska.
 * One AAA M2 at U.S. Army Ordnance Museum in transit to US Army Air Defense Artillery Museum, Ft. Sill, Ok.
 * One AAA at Broadalbin, New York
 * One AAA at Roswell, New Mexico
 * One AAA at Greenville, South Carolina
 * One AAA at Anderson, South Carolina VFW post
 * One AAA at Deming, NM Deming-Luna Museum
 * One AAA at Utah Beach D-Day Museum, Sainte Marie du Mont, France. This gun belonged to the 116th AAA Gun Battalion and was lost in the Channel 6 June 1944. The gun was recovered by locals after the war.
 * One AAA M1A3 (built 1954) at Raton, NM
 * One AAA M1A1 at US Army Air Defense Artillery Museum, Ft. Sill, OK
 * One AAA M2A2 at US Army Air Defense Artillery Museum, Ft. Sill, OK
 * One AAA M1A1 at 31st ADA Brigade, Ft. Sill, OK
 * One AAA M1A1 at Ft. Bliss Museum, Ft. Bliss, TX
 * One AAA M1A1 at National Electronics Museum, MD
 * Two Anti/Tank T-8 at National Armor & Cavalry Museum, Fort Benning, GA

Weapons of comparable role, performance and era

 * 8.8 cm Flak 18/36/37/41 : contemporary German anti-aircraft gun
 * Cannone da 90/53 : contemporary Italian anti-aircraft gun
 * QF 3.7-inch AA gun : contemporary British anti-aircraft gun, firing a heavier (28 lb) shell
 * 85 mm air defense gun M1939 (52-K) : contemporary Soviet anti-aircraft gun