120mm for Air Defense

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.

[youtube https://www.youtube.com/watch?v=pjD7DAGR3Do]

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.

5 thoughts on “120mm for Air Defense”

  1. The American 90mm was excellent, particularly in its refined form of the M2 gun on M2 carriage – excellent fuse-setting mechanism, but something too bulky for throwing around near the front lines. The complaint often leveled against the American 90mm guns, compared to the German 88s, is the lack of refined armor-piercing round. When first designed, the Ordnance Corps offered the 90mm gun for four roles – AAA, field artillery, anti-tank, and anti-ship (on different carriages of course). Many of the first M1s were issued to Coastal Defense units. For such role, an AP shot capable of dealing with destroyer-sized targets existed. Such would have worked over most German tanks of 1943, but a heavy AA gun firing at tanks was not something that fit well with doctrine at that time (those Tank Destroyer units were supposed to go in and knock out tanks, the AA guns were supposed to clear the skies). Though some were on hand in 1942, not until early 1944 were significant stocks of AP sent to the ETO. And still later for a refined APC AT round.

    IIRC, weren’t four of the 120mm M1s sent to Northern Ireland by mistake?

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