A stunning Navy decision to abort a $20 billion plan for a new fleet of destroyers yesterday threw into question the future of Raytheon Co.'s largest defense program and renewed longstanding concerns about the fate of the Bath Iron Works shipyard in Maine.

Waltham-based Raytheon is the prime contractor for the ship's combat systems, which are being developed at its Tewksbury and Andover plants. Assembly work on the guided-missile destroyers was to have been divided between the 124-year-old Bath shipyard, owned by General Dynamics Corp., and a yard in Mississippi. story continues..