A prototype reactor was built ashore at Knolls Atomic Power Laboratory's Kesselring Site in West Milton, New York in 1958 to test the reactor design. Once the design was proven, the prototype continued operation to train students and test new systems and materials. This prototype training reactor was taken off line in 1992 and subsequently decommissioned.
Although the design of the entire S3G reactor plant (core, piping, pumps, etc.) saw only limited use, a design version of the reactor core ("S3G3" or "S3G core 3") was later used for replacement cores for the Navy's 100 S5W reactor plants when refueled. Another unique feature of the S3G core 3 was the use of "Y" shaped control rods versus the standard cruciform control rods used in the S5W core. The core also utilized a rod configuration called "skewed divergent" for ease of maintenance.