A Panamanian freighter carrying guns and other equipment for Japan's Ground Self-Defense Force sank Monday afternoon off Miyagi Prefecture, the Japan Coast Guard said.
The 9,002-ton freighter Buen Viento, with 23 crew members aboard, was en route from Yokohama to the United States when it sank at around 3:50 p.m., the coast guard said, adding that the entire crew was rescued uninjured.
According to the coast guard, a rock drill -- which was not part of the GSDF equipment on the ship -- tore holes in both sides of the ship, causing it to rapidly take on water and sink.
The freighter tried to return to Japan but was unable to do so, as its bow was riding below the surface of the sea.
According to the Defense Agency, the equipment was being transported to the U.S. because the GSDF had planned to conduct shooting drills in Arizona from late May. The drills are now expected to be postponed.
The equipment was worth about 2.6 billion yen and included two heavy-duty guns worth roughly 300 million yen each, the agency said, adding that the loss will be covered by insurance.