WASHINGTON (Reuters) - A U.S. government watchdog said on Thursday that more than a third of U.S. Navy ships based out of Japan had expired warfare training certifications, as lawmakers raised concerns about readiness after a series of collisions involving the Navy this year.

The U.S. Navy recently removed Seventh Fleet Commander Vice Admiral Joseph Aucoin after a pre-dawn collision between a guided-missile destroyer and a merchant vessel east of Singapore and Malaysia in August, the fourth major incident in the U.S. Pacific Fleet this year.

In the latest incident, 10 sailors were killed after the USS John S. McCain collided with a merchant vessel in waters near Singapore and Malaysia, triggering a fleet-wide probe of operations and training.

In June, the USS Fitzgerald collided with a Philippine container ship, killing seven U.S. sailors.

Speaking before a House of Representatives Armed Services Committee hearing, John Pendleton, from the U.S. Government Accountability Office (GAO), said that a report had found that 37 percent of U.S. Navy cruisers and destroyers based out of Japan had expired warfare certifications as of June 2017. That was a five-fold increase from the number in May 2015.

The certification is a measurement of whether a ship and its crew are well trained and ready for operations.

The GAO report also found that a reduction in crew sizes was contributing to safety risks, with some sailors working over 100 hours a week and there was limited training because of an increased demand for operations.

“The Navy has made plans to revise operational schedules to provide dedicated training time for overseas-based ships, but this schedule has not yet been implemented,” the report said.

Admiral Bill Moran, deputy chief of naval operations, said that advanced technology was meaningless unless sailors were well trained.

“All of the marvelous technology, the magnificent hardware that we put together in these ships, and the power of our weapons systems are meaningless without well-trained, skilled, patriotic and experienced sailors who are well lead,” Moran said at the hearing.

Lawmakers expressed concern about the Navy’s readiness.

“These negative training trends clearly contributed to the lack of seamanship evident onboard the USS John McCain and the USS Fitzgerald,” Congressman Rob Wittman said.