The Navy's long-struggling littoral combat ship is sailing into summer on a tide of mixed signals and an uncertain future in the defense budget.

About the only thing that the Navy, White House and lawmakers agree on is that more of the unpopular and underperforming $556 million ships should be built.

Beyond that, the question for the coming months, when Congress finalizes its budget, is just how many will be ordered in 2018 from Lockheed Martin and Austal USA, the makers of the two variants.

House lawmakers have so far come in on the high end. The House Armed Services Committee, backed by members in the shipyard states of Wisconsin and Alabama, approved a defense policy bill late last month calling for three of the littoral combat ships, or LCS, which were designed to be a low-cost, shallow-water addition to the Navy fleet.

The LCS has been roundly criticized for not making good on its design promise of a shore-hugging, minimally-manned ship that can be outfitted with modules to fight surface, submarine and mine threats. It has suffered cost overruns, engineering problems and a lack of capabilities. House Armed Services Democrats called it a disaster, but failed to cut one of the ships from the committee's budget bill, which has not been approved by the full House.

Armed Services Republicans and analysts say, despite the ship's shortcomings, there is at least one good reason to keep buying them: The Navy's shipbuilding industrial base.

"The industrial base issue is a very real issue and if we aren't buying enough ships to keep the industrial base alive then it makes it exponentially more difficult at any point in the future to expand," said Chris Harmer, a senior naval analyst at the Institute for the Study of War. The monohull Freedom class is built at Fincantieri Marinette Marine in Wisconsin. The aluminum trimaran Independence class is built at Austal's yard in Mobile, Ala.

Rep. Bradley Byrne, an Alabama Republican whose district includes the Mobile shipyard, warned that anything less than three LCS hulls in 2018 would force layoffs for 10 to 40 percent of the skilled shipbuilding workforce and drive up future Navy ship costs.

Analysts such as Harmer say two is more likely the number needed to keep the Alabama and Wisconsin shipyards humming and ready to compete for a new Navy frigate, which is expected to begin production in the 2020s. Once yards downsize, it could be time-consuming and costly to spin them back up to capacity for the frigate production.

"It's got to be more than one a year. One a year is not going to be enough to sustain [the industrial base]," Harmer said.

The Navy has decided two is the right number, but only after some of its own mixed signals. Acting Navy Secretary Sean Stackley testified to a Senate committee in May that one LCS would be enough to keep the shipyards operating and healthy.

"My theory is they figured Congress would stick at least another one in at some point. Why spend that half a billion dollars in the budget when you know they are going to put it in later?" said Bryan McGrath, deputy director for the Center for American Seapower at the Hudson Institute. "Instead, they took half a billion dollars and spread it around to higher priorities."

But the White House intervened on the same day Stackley testified and the service clarified that it would instead request two LCS hulls. It sent an official budget amendment to Congress in late June.

McGrath says the sudden shift likely came down to President Trump's promise to vastly increase the size of the Navy during and after the campaign. Alabama is a deep red state that went big for Trump, and Wisconsin flipped Republican to seal his victory.

"When it went over [to Congress] as one ship, I think the Alabama and Wisconsin delegations and lobbyists went nuts and reminded the political side of the White House what the president's promises were and got a very short-noticed order to go over to the Department of Defense to fund that second LCS," McGrath said.

However, the Senate will also get its say in the LCS procurement debate, and Sen. John McCain's Armed Services Committee has put in the low-end request of just a single ship. Its version of the National Defense Authorization Act has not been approved by the Senate and will have to be reconciled with any House plans later this year.

McCain has long been a critic of the ship and last month called it one of the "greatest disasters" among defense weapons buying programs. He said the Navy should buy the minimum LCS number possible to keep the industrial base viable.

Senate Armed Services staff members say they found Stackley's original testimony about one LCS "compelling" while drafting the NDAA.

Taxpayer watchdog groups such as the Project on Government Oversight also see the ship as a boondoggle and a "big waste" of taxpayer money that is best avoided.

"When congressmen are making the industrial base argument for the LCS, they're basically telling us that the ship does not fit any real combat function," said Dan Grazier, a Jack Shanahan fellow at POGO. "They're basically giving up the ghost that the LCS isn't worth anything except as a practice venue for the shipbuilders."

Analysts are widely critical of the program, too, but some remain hopeful the ship can be improved and overcome some of its shortcomings.

Jerry Hendrix, senior fellow at the Center for a New American Security and a naval historian, says it may be too early to give up on LCS. He points out that the Oliver Hazard Perry-class frigates that the Navy deployed in the 1970s, and are now all gone, were once widely criticized.

"Today, we treat the Perry class as if it was the gold standard of frigates. Ships mature over time," Hendrix said.

Meanwhile, the Navy can continuing moving toward its new frigate replacement by buying two LCS hulls in 2018, he says, which would ensure the Marinette and Austal shipyards have continued operations and neither gains an advantage in 2018 over any future frigate bidding.

"Yes, LCS has got a lot of technical challenges, particularly in its propulsion plant. Hopefully, we can work those things out. But hopefully, we can get to this new frigate design as soon as possible," Hendrix said.