Two senior Navy commanders were relieved of duty Monday by Vice Admiral Phil Sawyer, the commander of the Japan-based Seventh Fleet, bringing the total number of fired commanders to six, including the top three officers of the Fitzgerald.

The US Government Accountability Office said in a report early this month that the Navy has "increased deployment lengths, shortened training periods, and reduced or deferred maintenance to meet high operational demands, which has resulted in declining ship conditions and a worsening trend in overall readiness."

The report said the crew are being overworked and undertrained but some vital maintenance is not being completed on time.

Spencer stressed that Congress has added training and other requirements to the Navy over time. "No one is taking a rock out and the rucksack is getting pretty damn heavy," he said.

Fatal training accidents have taken the lives of four times more service members than real combat has over the last three years, McCain said as he noted Congress' responsibility.

"Years of budget cuts, continuing resolutions and sequestration have forced our military to maintain a high operational tempo with limited resources," he argued.

US Defense Secretary Jim Mattis said on Monday he was reviewing if there was link between recent military accidents and budget caps.

"I am not willing to say right now that there is a direct line between sequestration and what has happened. I am willing to say we are going to take a very close look at that," he told reporters.