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Here are eight takeaways from ProPublica’s report on the Navy’s littoral combat ship program, which has cost taxpayers billions but failed to deliver on its promise.

1. Navy officials vastly underestimated the costs to build the ship in estimates provided to Congress. The original price tag more than doubled.

Contractors were supposed to build the ships fast, in large numbers and at an original cost of $220 million each — cheap for a Navy vessel. The ships were based in part on designs for commercial car or passenger ferries. As the Navy began to apply tougher standards, costs soared.

2. The ships were supposed to be equipped with interchangeable weapons systems to allow them to fight, hunt submarines and detect mines. The Navy failed to make this happen.

Former officers said that the Navy’s haste to deliver the ships took precedence over the vessels’ combat abilities. After spending hundreds of millions, the Navy abandoned its plan to outfit the ships to find and destroy submarines; the system to hunt undersea mines is still under development. Without functioning weapons systems, one former officer said, the ship was only a “box floating in the ocean.” In response to questions, the Navy acknowledged the LCS was not suitable for fighting peer competitors such as China. The LCS “does not provide the lethality or survivability needed in a high-end fight.”

3. Scores of sailors and officers spent more time trying to fix the ships than sailing them.

Because the crews were so small, only the most elite officers and sailors were meant to sail the ships. But breakdowns meant that the ships often spent more time in port than at sea. Some sailors sought mental health assistance because of the challenges. The LCS program became known as a place where naval careers went to die. Over time, the Navy increased crew sizes on the LCS.

4. The Navy relied so heavily on contractors for maintenance and repair that sailors and officers were unable to fix their own ships.

Sailors and officers were not allowed to touch certain pieces of equipment because of complicated arrangements with Navy contractors. Cumbersome negotiations meant it could sometimes take weeks to get contractors on board. “An average week would consist of 90 to 100 hours in port doing, honestly, nothing,” one former officer said of his time. The Navy has recently increased the amount of maintenance performed by sailors.

5. A string of high-profile breakdowns at sea beginning in late 2015 laid bare the limits of the ships and their crews.

In late 2015, the USS Milwaukee broke down en route to its home port, the equivalent of a brand new car stalling on its way out of the dealership. In January 2016, the USS Fort Worth broke down when a crew of exhausted sailors failed to execute a routine procedure, costing the Navy millions in repairs. Months later, the USS Freedom saw its engine destroyed by a seawater leak. Then the USS Coronado had trouble with its water jets, followed by the USS Montgomery, which collided with a tugboat, then cracked its hull after striking a lock in the Panama Canal. Each incident added fresh embarrassment to a program meant to propel the Navy into a more technologically advanced future.

6. Top Navy commanders pressured subordinates to sail even when the crews and ships were not fully prepared to go to sea.

On the Freedom, sailors and officers understood that they had a “no fail mission” with “‘no appetite’ to remain in port.” Even though one engine was contaminated, the ship’s commander took it to sea. Afterward, the ship needed repairs that took two years to complete and cost millions. On the Fort Worth, one sailor complained that there was “no break, no reprieve, just increasing daily tasking.”

7. One Navy secretary and his allies in Congress fought to build more of the ships even as they broke down at sea and their weapons systems failed. The Navy wound up with more ships than it wanted, at an estimated lifetime cost of $100 billion.

Time and again, senior officers voiced their concerns about the ineffectiveness of the ships, yet members of Congress, the Pentagon and Navy leaders advocated for them anyway. In some cases, officers assigned to review the ships’ performance saw their careers derailed after sharing their unvarnished, critical findings.

Former Navy Secretary Ray Mabus said the Navy took the breakdowns seriously, “but it did not seem, from what we were looking at, that it was a systemic problem.”

8. Lawmakers with shipyards in their districts played a key role in expanding the program and protecting it from scrutiny.

When the Navy decided to issue contracts to build 20 littoral combat ships in two states in 2010, it encountered stiff resistance from the then-ranking member of the Senate Armed Services Committee, John McCain, a Republican. But Sen. Richard Shelby, a Republican representing Alabama, where some of the ships were being built, slipped in an amendment that would allow the Navy to do so in a last-minute budget bill. “He made sure it happened,” a Shelby spokesman said at the time. Democratic Sen. Carl Levin of Michigan, who was initially skeptical of the ships, supported the proposal. He said the plan to build 10 vessels at a shipyard in neighboring Wisconsin would provide “a major boost for the region’s economy.” Even after the Navy finally determined that it only needed 32 of the ships, Congress managed to fund three more.

Kristen Berg, Mollie Simon and Joshua Kaplan contributed research.