The Largest Submarine in the U.S. Navy - USS Pennsylvania is a United States Navy Ohio-class ballistic missile submarine which has been in commission since 1989.
The Ohio class is a class of nuclear powered submarines used by the United States Navy.
The Navy has 18 Ohio-class ballistic missile submarines and guided missile submarines.
The Ohio class of nuclear-powered submarines is the sole class of ballistic missile submarines (SSBN) currently in service with the United States Navy.
Fourteen of the eighteen boats are SSBNs, 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 submarines (SSGNs).
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.