The Ohio class is the largest type of submarine ever constructed for the U.S. Navy, and are second only to the Russian Typhoon-class in mass and size. Ohio-class submarines were specifically designed for extended deterrence patrols. The class design allows the vessel to operate for 15+ years between overhauls. The ships are reported to be as stealthy at 20 knots (their cruising speed) as previous subs were at a dead crawl of 6 knots (11 km/h), although exact information remains classified.