Navy today exploded a World War II 16-inch unfused projectile that was found in the waters off Hapuna Beach on the Big Island’s Kohala coast.

The beach was reopened following the 10:30 a.m. operation.

Two experts from Pearl Harbor’s Explosive Ordnance Disposal Mobile Unit 3 and an Army ordnance specialist flew to the Big Island yesterday to help the state assess the situation.

The Navy hasn’t been able to determine its age or origin.

The project, which was eight inches in diameter, was embedded in the lava rocks, sand and marine growth at the beach.

 It caused no immediate danger, but because it could not be removed, a small explosive charge was used to explode it in place, the Navy said.

The southern half of Hapuna Beach had been closed since Monday while the northern half of the beach was open.

A Hawaii County Ocean Safety lifeguard spotted the object partially buried in the sand on the ocean floor Monday.