The USS North Dakota (SSN 784) is a Virginia-class attack submarine, a class of nuclear-powered fast attack submarines in service with the U.S. Navy. The submarines are designed for a broad spectrum of open-ocean and littoral missions. They were conceived as a less expensive alternative to the Seawolf-class attack submarines, designed during the Cold War era, and are replacing older Los Angeles-class submarines, 20 of which have already been decommissioned. The USS North Dakota is 377 feet long, has a crew of 134, a top speed of 25 knots (29 MPH), and, courtesy of the S9G nuclear reactor, has essentially unlimited distance for the next 33 years.