The Marines were armed with six 5-inch ( 0.13 m ) \ / 51 cal pieces , originating from the battleship USS Texas ; twelve 3 in ( 76 mm ) \ / 50 cal anti-aircraft guns ( with only a single working anti-aircraft director among them ) ; eighteen .50 in ( 12.7 mm ) Browning heavy machine guns ; and thirty .30 in ( 7.62 mm ) heavy , medium and light water - and air-cooled machine guns of various manufacture and operating condition .
There were also twelve 3 in ( 76 mm ) \ / 50 cal anti-aircraft guns , eighteen .50 in ( 12.7 mm ) Browning heavy machine guns , and thirty M1917 Browning machine guns .