The Navy's littoral combat ship is costing taxpayers billions more than budgeted, failing survivability assessments, and may never live up to the original vision for the program, a panel of Navy and government oversight officials told the Senate Armed Services Committee on Thursday.

The hearing, which focused on continued testing and acquisition of the small surface vessels, came at the close of a 12-month period in which five of the eight littoral combat ships in service have suffered major mechanical and engineering casualties. Navy officials have ordered dramatic program overhauls and reviews of ship employment and training in response to the breakdowns.

And despite the program's underperformance, costs continue to skyrocket, testified Paul Francis, managing director of acquisition and sourcing management at the Government Accountability Office. The ship's unit cost has more than doubled from $220 million to $478 million apiece, and plans to conduct a "block buy" of 12 redesigned littoral combat ships, to be called frigates, will put taxpayers on the hook for nearly $14 billion, he wrote in a GAO report released Thursday.

"The miracle of LCS didn't happen," Francis told the Senate panel. "... Once the money wheel starts to turn, the business imperatives of budgets and contracts and ship construction take precedence over acquisition and oversight principles."

In an era when other major-dollar acquisition programs such as the F-35 Joint Strike Fighter and the Gerald R. Ford-class carrier have dominated headlines on account of delays and budget overruns, the sternest rebukes in Congress may be reserved for the embattled LCS program.

"The experience of LCS, it broke the Navy," said Sean Stackley, assistant secretary of the Navy for research, development and acquisition. "... We have our program managers pretty much under a microscope right now, and we've taken things like cost and we've put cost into our requirements so that you don't get to ignore costs while you're chasing requirement. Just like speed, range, power and payload, if you start to infringe on the cost requirement that we put into our documents, you have to report to [Research, Development and Acquisition] and [the Chief of Naval Operations] just like you do if you infringe on one of the other requirements."

In prepared testimony for the hearing, the Pentagon's director of Operational Test and Evaluation, J. Michael Gilmore, gave a damning accounting of where the program stands, saying neither of the two LCS variants now being built by competing contractors is expected to be survivable in combat, a fact that undermines the whole concept of operations for the ship class.

Design failures also hobble the ship's effectiveness, he wrote in the 30-page document. The small crew size, he said, limited mission capabilities, combat endurance, and the ability of the crew to conduct major repairs without bringing in outside help. While a new crewing model introduced by the Navy in September will allow the ships to each focus on a single mission -- surface warfare, mine countermeasures, or asymmetric warfare -- Gilmore said his department does not yet have enough information to determine whether this approach will solve the problem.

In air warfare, he wrote, both ship variants lagged behind in testing, and it appeared unlikely that the LCS ultimately would be able to meet the Navy's air defense requirements.

"The need for this testing is all the more acute given the recent [anti-ship cruise missile] attacks against Navy ships off the coast of Yemen," Gilmore wrote, citing a series of incidents in October that prompted the Arleigh-Burke Class Destroyer Mason to fire missiles in self-defense.

In shock trials this summer with the littoral combat ship Milwaukee, designed to test the ship's ability to withstand an attack and keep fighting, the Navy had planned to conduct a traditional "three-shot" shock trial, with controlled blasts maxing out at only two-thirds the required shock level for the ship's design.

But the service stopped the trial after only two shots, Gilmore said, due to concerns that the third would "significantly damage substantial amounts of non-hardened equipment, thereby necessitating costly and lengthy repairs."

The Milwaukee was commissioned Nov. 21, 2015, and suffered a major engineering casualty less than a month later due to debris collection in the lube oil filter, requiring a 40-mile tow back to port.

The only voice on the panel who expressed unmixed optimism about the LCS was Vice Adm. Thomas Rowden, commander of Naval Surface Forces.

He was grilled by committee chairman Sen. John McCain, an Arizona Republican, who asked him to take responsibility for the engineering casualties that had happened on his watch, at least several of which were the result of engineer error.

"Should you be in your job?" McCain demanded.

"Yes sir, I believe I'm capable of fulfilling my responsibilities," Rowden replied. "What I did find was that training we had provided to the young men and women was insufficient. … I think we're in a much better place moving forward. We are going to start holding people accountable."

Pressed by the committee, Rowden said he believed the ships, deployed with sailors and Marines aboard, would hold up in combat.

Gilmore disagreed.

"You're never going to get from me, or anyone else, an honest, ironclad guarantee that the ships are going to perform the way people say they hope they will," he said.

-- Hope Hodge Seck can be reached at hope.seck@military.com. Follow her on Twitter at @HopeSeck.