A moored training ship (MTS) is a United States Navy nuclear powered submarine that has been converted to a training ship for the Naval Nuclear Power Training Command's Nuclear Power Training Unit (NPTU) at Naval Support Activity Charleston in South Carolina. The NPTU is part of the Navy's Nuclear Power School at Goose Creek, S.C. The Navy uses decommissioned nuclear submarines and converts them to MTSs to train personnel in the operation and maintenance of submarines and their nuclear reactors. The first moored training ship was USS Sam Rayburn (SSBN-635) a James Madison-class fleet ballistic missile submarine, redesignated as (MTS-635) in 1989, followed a year later by USS Daniel Webster (SSBN-626), a Lafayette-class ballistic missile submarine, redesignated as (MTS-626). Conversion of these two boats took place at the Charleston Naval Shipyard and modifications included special mooring arrangements with a mechanism to absorb power generated by the main propulsion shaft.^[1]

The Navy added two more moored training ships to this facility, USS La Jolla (SSN-701)^[2] and USS San Francisco (SSN-711),^[3] a pair of Los Angeles-class attack submarines. The conversions for these two took place at the Norfolk Naval Shipyard^[4] and they will then be taken to NSA Charleston. La Jolla became inactive in early 2015 and began the 32 month conversion to a training ship. Changes include having the hull cut into three sections, with the center section being recycled and the other two joined with three new sections, manufactured by Electric Boat, extending the overall length by 23 m (76 ft). The project was expected to be completed by the end of 2018.^[5] San Francisco arrived at Norfolk to begin her conversion in January 2018.^[4]

With the addition of La Jolla and San Francisco, the Navy will retire Sam Rayburn and Daniel Webster.^{[citation needed]} Sam Rayburn will be relocated to Norfolk Naval Shipyard in 2021, to remain there until the inactivation process begins, and Daniel Webster will also be inactivated at Norfolk, sometime later.^{[citation needed]}