Lashup Radar Network equipped with AN/CPS-5. M1 guns were deployed for the protection of nuclear production facilities, major industrial centers, strategic air force bases, and select major population centers. In 1954, the MIM-3 Nike Ajax surface-to-air missile became operational with ARAACOM. It substantially outranged the M1 gun, rendering it obsolete. ARAACOM began retiring the M1 gun from active-duty units and then from National Guard units. Then in 1957, the Soviet Union introduced the R-7, its first ICBM, and the M1 gun became practically useless. By January 1960, all remaining National Guard units with M1 guns were converted to Nike missiles or deactivated. Modification as tank gun Design studies began in early 1945 to modify the design of the M1 for use as an armament in heavy tank programs, the result of these being designated 120mm gun T53. Two T30 Heavy Tank chassis were diverted to fit the gun, resulting in the T34 Heavy Tank. Firing tests revealed issues with fumes from the gun entering the turret, causing flarebacks and a high concentration of toxic gases in the fighting compartment. As a result of this, the design of the gun was modified to fit a Bore evacuator. In 1948 a new heavy tank project T43, later to become the M103, was proposed to use a lightened version of the T53. This gun, 120mm gun T122, was balistically identical to the earlier model. The design was further evolved with the T123 design increasing the powder pressure from 38,000psi to 48,000psi, before finally introducing a quick change gun tube with the T123E1. In this form the design was standardised as 120mm gun M58, which would see service in production M103s. The British heavy tank program, FV214 Conqueror, used a modified version of the M58 design, designated Royal Ordnance L1. See also List of U.S. Army weapons by supply catalog designation (SNL D-32) Director (military) Rangekeeper Gun Data Computer Fire-control system Kerrison Predictor Weapons of comparable role, performance and era 12.8 cm FlaK 40 130 mm air defense gun KS-30 QF 4.5-inch Mk I – V naval gun Type 3 12 cm AA gun Notes References TM 9-2300 Standard Artillery and Fire Control Materiel dated 1944 TM 9-380 SNL D-32 External links World War II anti-aircraft guns Anti-aircraft guns of the United States Tank guns of the United States 120 mm artillery Weapons and ammunition introduced in 1944