Today in WW II: 28 May 1940 Belgium surrenders to Germany.  More 
28 May 1941 Blacked out destroyers make daring midnight trips to southern Crete ports, rescuing about 16,000 of the 50,000 British troops who had reached Crete from Greece [28-30 May].
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120mm Gun M1 Anti-Aircraft Artillery

The 120mm Gun M1 was developed for high-altitude anti-aircraft defense and was deployed in 1940 as World War II was on the horizon. It was originaly designated as the 4.7 inch mobile gun, but was renamed "120mm" as the War Department changed over to metric sizes in 1944. Only about 550 were produced and almost none left the United States during WW II although a few saw action in Korea. In March 1950 batteries of 120mm guns deployed to protect the plutonium production plant at Hanford, WA. The year 1953 was the peak year for the number of l20mm battalions with 14 deployed, a total of 224 guns. The 120mm Gun M1 served into the late 1950s when it was replaced by the Nike Ajaz missile system.

The M1 120mm Gun was mounted on the eight-wheel M1 antiaircraft carriage, weighing about 31 tons with a 13-man crew. Its maximum vertical range was about 58,000 feet. Under good conditions a 120mm gun could deliver 20 seconds of effective fire on a conventional airplane flying at an altitude of 40,000 feet. The rate of fire was from 10 to 15 rounds per minute, depending on three principal factors: state of training of the gun crews, whether or not mechanical time fuzes were being used and the magnitude of the fuze being set. The projectile weighed 50 pounds.

The massive 120mm gun was classified as "mobile", but it could be moved only when there were good roads and bridges plus plenty of time.

120mm Anti-Aircraft mobile gun for 85th Anti-aircraft Artillery Gun Battalion, Fort Story, VA, secured to railroad flat car at Norfolk Army Base, Norfolk, VA, 10 April 1944
120mm Anti-Aircraft mobile gun for 85th Antiaircraft Artillery Gun Battalion, Fort Story, VA, secured to railroad flat car at Norfolk Army Base, Norfolk, VA, 10 April 1944.

Enlisted personnel of Battery D, 36th Anti-aircraft Artillery Gun Battalion undergoing training at Fort George G. Meade, February 1953.
Enlisted personnel of Battery D, 36th Anti-aircraft Artillery Gun Battalion undergoing training at Fort George G. Meade, February 1953.