Shortly before 10 p.m. on July 19, 1972, two waves of MiG-17 fighters attacked the guided missile frigate USS Biddle. Two MiGs came in the first wave. The ship’s Terrier surface-to-air missiles downed one and sent another scrambling.

The three-MiG second wave, detected at about 8 miles, came in low at about 580 mph and quickly got too close to hit with a missile launch. With no working radar to direct the Biddle’s gunfire, the ship’s guns opened up with a World War II style barrage (at a low angle and high volume).

During a period of just 90 seconds, 54 5-inch and 35 3-inch rounds were fired. One MiG was shot down. Another headed home. The third flew overhead without dropping any bombs. The ship fired two Terriers at the fleeing MiGs but failed to hit them.

The Biddle’s action marked the Vietnam War’s only successful downing of an enemy aircraft by naval gunfire.

The weapon credited with that success, the Biddle’s 3-inch/50-caliber cannon, was developed after World War II to increase shipboard anti-aircraft firepower and range. The Mark 22, first produced in 1948, fired the same ammunition and used the same barrel as its semi-automatic 3-inch/50 predecessor.

With the Mark 22’s automatic cannon, two crewmen—one on each side of the gun—loaded rounds into a rotating sprocket that rolled into alignment with the breech. A ram then drove the round into the breech, which closed and fired it when the cartridge tripped an ejector. The breech opened during the recoil stroke, dropping the expended round onto a tray and then onto the deck, and the process was repeated.

Installed on all ocean-going American warships, auxiliaries and Coast Guard cutters as well as patrol ships given to Saigon, the Mark 22 was at one time the U.S. Navy’s most numerous artillery weapon.

The 3-inch/50, employed almost exclusively against visible targets ashore during the Vietnam War, was succeeded by the shorter-ranged but deadlier Phalanx close-in-weapons system in 1980. V

This article appeared in the February 2021 issue of Vietnam magazine. For more stories from Vietnam magazine, subscribe here and visit us on Facebook: