Named after its lead boat, the Ohio class of nuclear-powered submarines is, as of October 2013, serving with its sole operator, the United States Navy. Fourteen of the eighteen boats are ballistic missile submarines (SSBN), which, along with U.S. Air Force strategic bombers and intercontinental ballistic missiles, constitute the nuclear-deterrent triad of the U.S. The remaining four have been converted from their initial roles as SSBNs to cruise-missile carriers (SSGN). The Ohio-class boats, each displacing 18,750 tons submerged, are the third largest submarines in the world, behind the 48,000-ton Typhoon class and 24,000-ton Borei class of the Russian Navy. The Ohio class replaced the Benjamin Franklin- and Lafayette-class SSBNs.