Japanese navy divers detonate 461 U.S.-made shells believed to be from World War II in Nakagusuku Bay, Okinawa, Feb. 13, 2025. (Brian McElhiney/Stars and Stripes)

URUMA CITY, Okinawa — Japanese troops exploded 461 U.S.-made shells off the coast on Thursday, the latest in a continuing stream of World War II leftovers that turn up on the former island battleground.

Eleven explosive ordnance disposal divers with the Japan Maritime Self-Defense Force’s Sub Area Activity Okinawa unit detonated the shells a mile offshore of Nakagusuku Bay Port, according to a Self-Defense Force spokesman. The detonation took place at 10:50 a.m.

The divers installed a plastic bomb to detonate the shells 36 feet below the surface, the spokesman told Stars and Stripes before the operation began.

The shells were discovered over the past two to three years in and around Nakagusuku Bay, according to a spokesman with the city’s Crisis Management Division. Some were found by construction vessels during dredging work, while others were discovered by civilians swimming in the area.

According to a document shown to Stars and Stripes by the city spokesman, the ordnance included one 5-inch shell, one Type 90 shrapnel, one 57 mm field gun shell, one 60 mm trench mortar round, two 81 mm trench mortar rounds, 13 20 mm field gun shells, five 37 mm field gun shells, 237 12.7 mm machine gun rounds, and 200 7.62 mm rounds.

The shells collectively weighed 264 pounds, according to a Jan. 30 Uruma city news release.

Japanese troops last detonated a collection of ordnance off Okinawa about two years ago, the Self-Defense Force spokesman said.

“This time, the amount is larger because there are a lot of small bullets, but the weight is almost the same,” he said.

The shells were stored in an underwater metal cage in the bay away from swimmers and boaters until Thursday’s detonation, he added.

Some Japanese government officials speak to the press only on condition of anonymity.

The detonation followed multiple recent discoveries of unexploded ordnance believed to be from WWII on Okinawa.

On Feb. 6, five members of the Ground Self-Defense Force’s 101st Explosive Ordnance Disposal Unit removed a U.S.-made, 5-inch shell from a warehouse construction site inside the Maritime Self-Defense Force’s air base in Naha city, a spokesman with the city’s Disaster Prevention and Crisis Management Division said by phone Thursday.

The soldiers moved the shell into an explosion-proof container using a crane and defused it without issues, the spokesman said.

The Japanese government has ramped up searches for unexploded ordnance at airports across the country. The government began surveys in October at Miyazaki Airport on Kyushu, the southernmost of Japan’s four main islands, after a WWII-era bomb exploded on a taxiway that month.

Magnetic surveys began in December at Naha Airport, along with airports in Sendai, Matsuyama and Fukuoka.