Navy leaders acknowledged Tuesday several unsettling truths about the service’s dangerous deployment pace and the role physical exhaustion — some sailors routinely endure 100-hour workweeks, they said — may have played in two deadly collisions at sea.

While leading a hearing of the Senate Armed Services Committee, Sen. John McCain (R-Ariz.) demanded answers and accountability for a string of recent mishaps, to include three collisions and a grounding, that have exposed the Navy’s struggle to address widespread leadership shortcomings and the erosion of training standards.

“As leaders of our Navy, you must do better,” McCain admonished Navy Secretary Richard V. Spencer and Chief of Naval Operations John M. Richardson during a hearing to learn what the service is doing to restore confidence in its surface warfare fleet and correct glaring questions about its commanders’ ability to hone seamanship and readiness amid constant deployments.

During his opening remarks, McCain, whose familial ties to the Navy span multiple generations, read aloud the names of several honored guests in attendance. They included the mothers, fathers and spouses of the 17 sailors killed this year.

“Your presence here today reminds us of our sacred obligation to look after the young people who serve in our military,” McCain said, noting his personal connection with the USS John S. McCain, a guided-missile destroyer named after his father and grandfather.

The ship collided with an oil tanker in a bustling sea transit lane near Singapore, killing 10 sailors on Aug. 21. Two months prior, the USS Fitzgerald, also a guided-missile destroyer, collided with a container ship in Tokyo Bay. That accident left seven sailors dead.

“We will identify shortcomings, fix them and hold people accountable,” McCain said, shifting his focus to Spencer and Richardson.

Global demand for Navy assets has soared since the United States went to war in 2001, but its number of ships has been cut by 20 percent since then, the officials said. Faced with persistent threats from North Korea and China’s growing empirical ambitions, U.S. commanders have leaned on the Navy to maintain a steady, robust presence in the Western Pacific.

The McCain and the Fitzgerald both belong to the Navy’s 7th Fleet, which is headquartered in Japan, and what befell their crews brings into stark focus how more missions in this region have left the Navy spread thin, hobbled by too few ships and worn-out, undertrained crews.

With a current fleet of 276 vessels, the service has taken considerable risk, officials say. They’ve argued it would require about 350 ships to meet minimum needs.

Richardson shifted some blame to Congress, saying the pressure Navy commanders feel to meet high operational demands has been exacerbated by automatic military spending cuts mandated by lawmakers. This impedes training schedules and budgeting for new ships and modern weapons, the admiral said.

But Richardson also acknowledged that commanders at every level of the Navy share responsibility for these recent mishaps.

“At the core, this issue is about command,” he said, which includes the spiraling consequences of a “can-do” culture that agrees to take on missions despite perilous gaps in training and certifications designed to measure how ready ships and sailors are for combat. The Navy has sacked at least half a dozen commanders following the four accidents this year, including the 7th Fleet commander, a three-star admiral — part of at least 20 reprimands of sailors across three ships.

McCain and other lawmakers on the armed services committee honed in on a critical new report, released Tuesday by the Government Accountability Office, highlighting the 100-hour weeks being worked by many sailors, a burden that erodes time needed for training and rest. Richardson told McCain he does not deny sailors commonly work those hours.

“There is a cultural factor here, where you’re more dedicated if you can stay awake,” Richardson said. “It’s like pulling an all-nighter in college.” Exhaustion leads to a “corrosive effect” on decision-making and performance, he added, noting that studies are being conducted to examine how schedules can be rectified.

“If we’re pointing out that sailors are working 100-hour weeks, I’m not sure we need a study,” McCain shot back.

John H. Pendleton, a defense readiness expert with the Government Accountability Office, bluntly acknowledged during his testimony the extremes some personnel take to man their ships and aircraft. Sailors, he said, “wish for a 100-hour week.”

The watchdog published another report in June that found combat certifications had lapsed for nearly 40 percent of cruisers and destroyers ported in Japan — a fivefold increase since 2015.

Reports also found ship staffing cutbacks since the 2000s have led to safety risks, along with maintenance windows prolonged by older ships outliving their intended life spans. About 60 percent of 169 surface ships were out of commission for 6,603 operational days from 2011 to 2016, the report said, or about 18 years-worth of training and mission time.

In a stern closing statement, McCain warned that such a relentless operational tempo not only risks driving away talent, it sets the conditions for human error. He implored Navy leaders to inject “common sense” into their overhauls.

“I think I know what 100-hour weeks does to people over time,” he told Richardson, exasperated at the pace of change when everyone in the room acknowledged exhaustion was a central reason for the Navy’s troubles.

“You could make the change tomorrow,” he said.

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