ジェネラル・ダイナミクス・エレクトリック・ボート
Block IV involved 10 boats. In 2013, execution of this 10-submarine contract was put in doubt by budget sequestration in 2013. The most costly shipbuilding contract in history was awarded on 28 April 2014 as prime contractor General Dynamics Electric Boat took on a $17.6 billion contract for ten Block IV "Virginia"-class attack submarines. The main improvement over the Block III is the reduction of major maintenance periods from four to three, increasing each boat's total lifetime deployments by one.