The U.S. Navy awarded General Dynamics Electric Boat with a $21.1 million contract modification for reactor-plant planning yard services for nuclear submarines.

Electric Boat, a subsidiary of General Dynamics, was initially awarded the planning contract in November 2011, bringing the cumulative contract value to $121.2 million through 2016 given the parties go through with all planned options. The maintenance work will be performed on moored training ships in both Groton, Conn., and Charleston, S.C.

Electric Boat's engineering and design division is comprised of 4,400 employees the company says are trained for construction, maintenance, and modernization for submarines. The company is based in Groton, New London, Conn., and Quonset Point, R.I.

General Dynamics is a global defense, aerospace, and maritime manufacturer headquartered in Falls Church, Virginia. The company reported over $30 billion in revenue in 2014.