According to Wikipedia: "The Ohio Replacement Submarine (formerly the SSBN-X Future Follow-on Submarine) is a future United States Navy submarine designed to replace the Trident missile-armed Ohio-class ballistic missile submarines. The United States Department of Defense anticipates a continued need for a sea-based strategic nuclear force. The current Ohio class is expected to retire its first vessel by 2029, resulting in an expectation that a new platform must be seaworthy by that time."