CAMP FOSTER, Okinawa — Okinawa fishermen heading toward their favorite fishing grounds Thursday were surprised by an unannounced military exercise taking place in the waters off Camp Schwab.

The fishermen were barred from the area.

Anti-base activists who monitor activity in the area complained to Nago City officials after learning of the incident. The U.S. military usually announces such exercises in advance.

The news surprised Nago officials, who said they were not notified and in turn notified the Naha Bureau of the Defense Facilities Administration, which called the Marine community-relations office on Camp Foster to find out what was going on.

The Marines there said they didn’t know, either.

The Navy amphibious group with Okinawa’s 31st Marine Expeditionary Unit was not expected to return to Okinawa from an exercise in the Philippines until later this month. But the ships and the buzzing of helicopters overhead announced the fleet had arrived early and decided to hone its warfighting skills a bit more.

“Normally, we are notified of any U.S. military training conducted in restricted waters at least 24 hours in advance, according to a regulation agreed between the governments,” said a spokesman for the Defense Facilities Administration Naha Bureau on Friday.

“But this time there was no notification,” he said.

Pictures of the USS Essex, with a swarm of helicopters overhead, were featured prominently in Okinawa newspapers Friday morning. Essex is the flagship of the amphibious readiness group.

“Prior notification is important for the safety of fishermen who operate in the waters,” the DFAB spokesman said. “The Marine Corps G5 office [community relations] offered an apology when we made an inquiry about the training.

“They told us that Marine Corps headquarters ordered the unit to immediately halt the training,” he said.

The Consolidated Public Affairs office on Camp Foster had no comment Friday concerning the exercise.