USS Sam Rayburn (SSBN/MTS-635) was a James Madison-class ballistic missile submarine named for U.S. House Speaker Sam Rayburn (1882–1961).
Sam Rayburn was decommissioned on 31 July 1989 and reclassified a moored training ship with hull classification symbol MTS-635. Stricken from the Naval Vessel Register on the following 28 August, she arrived at the Naval Nuclear Power School, Goose Creek, South Carolina, on 1 February 1986, and on 29 July 1989 achieved initial criticality in her new role. Her modifications included special mooring arrangements including a mechanism to absorb power generated by the main propulsion shaft (Water Wheel). She is scheduled to operate as an MTS until 2018 while undergoing shipyard availabilities at five year intervals.