The Army said Friday it recovered 74 pieces of decades-old unexploded ordnance from the ocean floor off Oahu’s Waianae Coast during a three-week effort to clear out most of the munitions the military dumped in the area years ago.

The cleanup also recovered 2,300 small-arms munitions, U.S. Army Garrison Hawaii said in a news release. The Army left alone munitions so encrusted with coral that removing them would have damaged the reef.

Using a remote controlled robot, the cleanup team attempted to recover more than 150 items that appeared to be weapons. It got 80 of these, but six turned out not to be munitions.

It destroyed more than 330 pounds of explosives, 135 pounds of propellant and all of the small-arms munitions recovered.

The weapons were found in an area so littered with munitions that it’s called Ordnance Reef.

The munitions are thought to be from World War II and were likely dumped in the ocean after the war. The military threw out its old weapons in the sea up to 1970 because it thought doing so was safer than burying them in the ground or burning them.

Ordnance Reef starts about a quarter-mile off the Waianae Coast. The weapons were most heavily concentrated in an area about a mile offshore. Lengthwise, they were found about 2 miles in the north-south direction off Pokai Bay and the Waianae Wastewater Treatment Plant.

The military used a robot instead of divers to recover the weapons as an experiment.

Early results of the project indicate the technologies used might both mitigate the safety risks of removing explosives from water as well as reduce the impact a removal effort would have on the environment, the Army said.