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The Marine Defense Battalions used four different cannons for coastal defense.

The 3-inch/50-cal, Mark 21, Mod 0 was standardized in 1939. It was nicknamed the "3-inch Navy". It weighed in at 7,510lbs and had a maximum range of 14,000 yards. It could fire HE, AP, shrapnel and Illum rounds at a rate of fire of 18rpm. This was a former navy gun removed from various ships.

The main stay of the USMC cd guns was the 5-inch/51-cal, Mark 15, Mod 0. It was standardized in 1938. Nicknamed the "Five-incher" it weighed 23,400lbs. Maximum range was 17,100 yards, It could fire Common HE, High Capacity HE, AP and Illum rounds. Rate of fire was 20rpm. This was another former navy gun, being removed from older battleships as they were modernized.

The largest gun in the USMC arsenel was the 7-inch/45-cal Mark 2, Mod 0. Standardized in 1939. This gun weighed in at 50,500lbs and had an effective range of 16,500 yards. It could fire HE and AP rounds. Rate of fire was 5rpm. There were 12 of these in service, removed from the predreadoughts Connecticut, Mississippi and Vermont prior to World War One and intended for use by the 10th Regiment in France as heavy artillery, these guns never left the US. They were emplaced on Midway, Johnson and Palmyra Islands. USMC records indicate two 2-gun batteries on each island, Navy records say two 1-gun batteries on each island with the rest in reserve at Pearl Harbor.

The above mentioned guns were used until 1943 when the were replaced by the M-1A1 155mm gun. Nicknamed the "Long Tom", it weighed 30,100lbs. Unlike the former navy guns, the 155mm could be towed to different positions. Its maximum range was 25,715 yards and it could fire HE, WP, High Capacity HE, and Illum rounds. Rate of fire was 3rpm.