120 mm M1 gun

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A 120 mm M1 anti-aircraft gun at Fort Meade in February 1953.

The 120 mm Gun M1 was the US Army's standard super-heavy anti-aircraft gun, complementing the smaller and more mobile 90 mm M3 in service. Its maximum altitude was about 60,000 ft, which garnered it the nickname the stratosphere gun. 120's served primarily in US defensive roles, although it had been designed to be mobile and saw some action during the Korean War. The 120 was phased out quite quickly in the 1950s with the introduction of the first truly effective missile systems, notably the Nike Ajax.

[edit] History

The Army had originally attempted to make a 120 mm design just after the end of World War I, with a prototype being presented in 1924. The system was considered far too heavy and expensive to be useful, and the project slowed down, although it was never cancelled outright.

In 1938 the Army started studying its needs for newer AAA systems, and decided to order new systems for both the heavy and super-heavy role. The former was filled by the new 90 mm gun, which replaced the earlier 3-inch gun then in use, while work on the 120 was dusted off and mated to a new eight-wheel carriage to produce the 4.7-inch M1 when it was accepted in 1940.

Only a small number of 120's were built, about 550 in total. They were mostly used on fixed mounts at various points around the continental US, although about fifteen were shipped to the Canal Zone to replace the semi-experimental 105 mm M3 gun that had filled this role. Four were sent, perhaps by mistake, to Northern Ireland. No 120 was ever fired at an enemy aircraft. In 1944 the gun was renamed as the 120 mm Gun M1, as metric naming became the standard.

Like the 90 mm, the 120 was typically operated in a battery of four guns, initially with an associated searchlight and SCR-268 radar, and later with the much-improved SCR-584 radar and M9 predictor that automatically laid the guns as well.