The Navy risks encountering cost increases on the Littoral Combat Ship (LCS) program because it’s buying systems for the class’s mission modules that are not fully developed and have “significant” performance problems, the Government Accountability Office (GAO) said in a report released Thursday.

The GAO examined the LCS program in a broader report focused on the Pentagon’s largest acquisition programs, including the mine countermeasures (MCM), surface warfare (SUW) and anti-submarine warfare (ASW) mission modules for the ships designed for close-to-shore operations. The mission packages are intended to be swappable onto and out of the ships.

The GAO applauded the Navy’s strategy to produce the mission modules in technological increments, but said there is still a risk of cost growth because some of the systems are not adequately mature and or have not been sufficiently tested.

“The Navy stated it is using an incremental approach to field mature systems and deliver periodic improvements in capability,” the GAO said. “However, the Navy continues to buy systems that are still in development, demonstrating significant performance issues, and not meeting all requirements–a practice that we have previously shown increases costs.”

The remote minehunting system and airborne laser mine detection system in the MCM package have both run into problems, the GAO said.

The Navy told the GAO in its response that the incremental approach allows it to advance the technology at a “natural pace” while providing it with the flexibility to move away from systems that do not meet cost, schedule or performance requirements.