Two top senators on defense issues say U.S. Navy leaders should consider delaying deployment of the new littoral combat ship (LCS) and tone down their effusive rhetoric about the vessel until it successfully completes more testing.

With six ships of a planned 40 delivered, but "practically no LCS mission capabilities proven" for mine clearance, surface warfare and submarine-hunting, "we urge you to re-evaluate the deployment strategy," John McCain, chairman of the Senate Armed Services Committee, and Jack Reed, the panel's top Democrat, wrote in a letter dated Friday.

As part of the Obama administration's promised "pivot to the Pacific," the navy has sent one littoral combat ship to Singapore with plans to have a total of two there by December and four by 2018. The vessel already in place, the USS Fort Worth, has been sidelined since a major crew-caused maintenance failure in January. The navy also plans to use littoral ships, intended for operations in shallow coastal waters, in Pacific exercises and for a deployment to Bahrain in 2017.