WASHINGTON, Sept. 19 -- Top leaders of the U.S. Navy were urged to do better on Tuesday as they appeared before a Senate hearing over a series of deadly ship collisions involving the Pacific fleet.

"We must also call you to task and demand answers. As leaders of our Navy, you must do better," Senator John McCain, head of the Senate Armed Services Committee, told Navy Secretary Richard Spencer and Chief of Naval Operations Admiral John Richardson.

The hearing was held in the wake of several Navy ship collisions, including one in August in which USS John S. McCain, a guided-missile destroyer, collided with an oil and chemical tanker near Singapore, leaving 10 U.S. sailors dead and five injured.

The highly-publicized incident came after seven sailors were killed when the USS Fitzgerald, also a guided-missile destroyer, and a container ship collided off the coast of Japan in June, along with two other non-deadly collisions involving the Navy vessels also this year.

McCain said those incidents are "preventable" but now it will cost an estimate of 600 million U.S. dollars for repairs.

"It is simply unacceptable for U.S. Navy ships to run aground or collide with other ships," the Republican senator said. "To have four such incidents in the span of seven months is truly alarming."

Richardson told the hearing that the Navy was conducting reviews and probes, while blaming the incidents on "the corrosive confluence of high operational tempo, inadequate budgets and budget uncertainty."

"But make no mistake, sir, while these factors do exert a negative force on the challenges we face, at the core, this issue is about leadership, especially command," Richardson said.

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 U.S. 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.

U.S. 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.

WASHINGTON, Sept. 19 -- Top leaders of the U.S. Navy were urged to do better on Tuesday as they appeared before a Senate hearing over a series of deadly ship collisions involving the Pacific fleet.

"We must also call you to task and demand answers. As leaders of our Navy, you must do better," Senator John McCain, head of the Senate Armed Services Committee, told Navy Secretary Richard Spencer and Chief of Naval Operations Admiral John Richardson.

The hearing was held in the wake of several Navy ship collisions, including one in August in which USS John S. McCain, a guided-missile destroyer, collided with an oil and chemical tanker near Singapore, leaving 10 U.S. sailors dead and five injured.

The highly-publicized incident came after seven sailors were killed when the USS Fitzgerald, also a guided-missile destroyer, and a container ship collided off the coast of Japan in June, along with two other non-deadly collisions involving the Navy vessels also this year.

McCain said those incidents are "preventable" but now it will cost an estimate of 600 million U.S. dollars for repairs.

"It is simply unacceptable for U.S. Navy ships to run aground or collide with other ships," the Republican senator said. "To have four such incidents in the span of seven months is truly alarming."

Richardson told the hearing that the Navy was conducting reviews and probes, while blaming the incidents on "the corrosive confluence of high operational tempo, inadequate budgets and budget uncertainty."

"But make no mistake, sir, while these factors do exert a negative force on the challenges we face, at the core, this issue is about leadership, especially command," Richardson said.

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 U.S. 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.

U.S. 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.