When you mention a 120mm gun today, virtually everyone thinks of the main gun of the M1 Abrams family of tanks. And rightly so. It’s an impressive weapon. But did you know that from the mid-1940s to the early 1950s there were more than a few 120mm guns guarding the US?
The US Army began World War II with the M3 3” gun as its primary heavy antiaircraft gun. The M3 was itself a slightly improved version of the M1918 fielded for World War II, and was clearly facing obsolescence. It lacked the ability to reach the high altitudes routinely used by enemy bombers, and didn’t throw a very powerful shell.
Soon the excellent M1 90mm anti-aircraft gun replaced it.
But as good as the M1 90mm gun was, it still lacked the range and altitude needed. Toward the end of the war, the Army finally fielded the massive M1 120mm heavy anti-aircraft gun. While a few batteries were sent to the Pacific before the war ended, it doesn’t appear any actually engaged Japanese aircraft.
The beginning of the Cold War raised the spectre of Soviet bombers laying waste to American cities with nuclear weapons. Accordingly, a very high priority was given to air defense of the continental US. The Air Force fielded many squadrons of fighters. And pending the development of guided missiles, the Army placed batteries of 90mm and 12omm guns to protect our cities.
A typical 120mm battery had four guns. The guns were automatically directed by the M10 director system, which in turn used information from the SCR-584 radar, or a similar gun laying radar and the M4 gun computer.
Batteries also protected sensitive sites such as the Panama Canal.
By the mid-1950s, the M1’s ability to destroy high speed bomber targets was marginal. As rapidly as possible, gun batteries were replaced by Nike Ajax guided missile batteries. Today, the M1 is but a faint memory.