Northrop Grumman Corp. and General Dynamics Corp., the U.S. Navy’s two largest shipbuilders, are reviewing their work on Virginia-class nuclear submarines after defects were found on weapons-handling systems of four vessels.

The companies have discovered improperly drilled and machined bolt holes, bolts that had been wrongly machined and fasteners that weren’t installed correctly, Alan Baribeau, a Navy spokesman, said in an e-mail Monday. The companies will deliver their combined review to the service in two weeks, he said.

The Virginia, at a cost of almost $2 billion a ship, is the newest class of U.S. nuclear-powered submarine and is designed to be able to fire Tomahawk cruise missiles, attack ships and conduct reconnaissance against land targets. The companies jointly won a $14 billion contract for eight more of the ships in December. General Dynamics is the prime contractor for the program. The weapons-handling systems under review are made by Northrop at its yard in Newport News, Virginia.

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