America's current Fleet Ballistic Missile Submarine. Since the first Poseidon submarines took to the seas in 1960, the sole purpose of the Fleet Ballistic Missile Submarine has been strategic deterrence. Given their wide operational area (70% of the world's surface is covered by water) the SSBN represents the most survivable and unreachable "leg" of America's land, sea, and air nuclear deterrence tripod. Built to accommodate the Improved Trident I ballistic missile and relying on advances pioneered by the Narwhal's natural circulation reactor as well as the advanced sensor capabilities of the Los Angeles class fast attack submarines, the Ohio class SSBNs are the most advanced ballistic missile submarines in the world. Virtually undetectable at operating speed and depth, the Ohio class SSBN can maneuver with impunity through the world's oceans and given the submarine's sensory capabilities an Ohio class boat will detect and maneuver around any threat long before the threat can acquire the SSBN. Of the eighteen Ohio class SSBNs currently in service, the first eight were designed to fire 24 Trident I Submarine Launched Intercontinental Ballistic Missile (SLICBM) each of which carries 10 Multiple Independent Reentry Vehicle (MIRV) warheads. The remaining ten were designed to carry the more powerful Trident II SLICBM each of which carries 12 MIRVs. Current Strategic Arms Limitation Treaty (SALT) conditions limit the number of MIRVs to eight per missile. In 1992 the Strategic Arms Reduction Treaty (START II) was signed, limiting member nations to 14 SSBNs each. As a result, only four of the original eight will be backfitted with the Trident II missile, while the rest will either be converted to SSGN cruise missile boats, Special Operations support ships (similar to the SSN640 class) or decommissioned.
The concept of technical superiority over numerical superiority was and still is the driving force in American submarine development. A number of Third World countries are acquiring modern state-of-the-art non-nuclear submarines. Countering this threat is the primary mission of U.S. nuclear attack submarines.
Their other missions range from intelligence collection and special forces delivery to anti-ship and strike warfare. The Navy began construction of Seawolf class submarines in 1989. Seawolf is designed to be exceptionally quiet, fast well-armed with advanced sensors. It is a multi-mission vessel, capable of deploying to forward ocean areas to search out and destroy enemy submarines and surface ships and to fire missiles in support of other forces.
The first of the class, Seawolf (SSN 21), completed its initial sea trials in July 1996. Attack submarines also carry the Tomahawk cruise missile. Tomahawk launches from attack submarines were successfully conducted during Operation Desert Storm.
In late 1998, the contract was let for building the first of the New Attack Submarine. This class, the Virginia-class fully embraces the new strategic concept in ... From the Sea and Forward... From the Sea. It is the first U.S. submarine to be designed for battlespace dominance across a broad spectrum of regional and littoral missions as well as open-ocean, "blue water" missions. The Virginia-class achieves the right balance of core military capabilities and affordability.
The Benjamin Franklin-class were converted from Fleet Ballistic Missile submarines and carry drydeck shelters. They are equipped for special operations and support SEALs. The former missile spaces have been converted to accommodations, storage, and recreation spaces.