The 120 mm Gun M1 was the United States Army's standard super-heavy anti-aircraft gun, complementing the smaller and more mobile M2 90 mm gun in service. Its maximum altitude was about , which garnered it the nickname the stratosphere gun. The 120 served primarily in static defensive roles, although it had been designed to be mobile. One battalion, the 513th AAA Gun Battalion, did make it to the Philippines in February 1945, although they never fired their guns in anger. There is also speculation that some 120s arrived in England in early 1945 to provide air defense for London, although no concrete evidence of this has been documented. The M1 gun was used in air defense, from 1944 through the early cold war period when the system was gradually phased out with active duty units,beginning in