This is the latest accident to befall the 7th Fleet, which is based in the Japanese port of Yokosuka, south of Tokyo, and has endured multiple collisions at sea this year, including two involving guided-missile destroyers that left 17 sailors dead.

The C2-A Greyhound aircraft was on a routine flight from Marine Corps Air Station Iwakuni in southern Japan to the USS Ronald Reagan aircraft carrier, which is currently in the Philippine Sea on exercises with Japan’s Maritime Self-Defense Force.

It crashed at 2:45 p.m. local time Wednesday, the 7th Fleet said in a statement. The cause of the crash was not immediately known and an investigation would be carried out, it said.