An S2G was the initial power plant of USS Seawolf (SSN-575). This was one of three sodium cooled fast reactors ordered for the Seawolf program at the same time as three PWR units were ordered to support the USS Nautilus (SSN-571) program; In each case, one reactor was land-based for training and research, one intended for installation on a submarine, and one spare. The land-based unit corresponding to S2G was S1G reactor.
Persistent superheater problems on Seawolf caused the superheaters to be bypassed, resulting in mediocre performance. This and concern for the dangers posed by liquid sodium coolant led to the PWR type being selected instead as the standard US naval reactor type, and the S2G on Seawolf was replaced by the spare S2Wa reactor from the Nautilus program.