- S = Submarine platform
- 6 = Sixth generation core designed by the contractor
- G = General Electric was the contracted designer
This nuclear reactor was designed by General Electric for use on the Los Angeles class attack submarines. The S6G reactor plant consists of the reactor coolant, steam generation, and other support systems that supply steam to the engine room. The 688-class engine room also contains the steam turbines that generate electricity and drive the propeller shaft. While exact specifications are classified, the S6G reactor can propel a Los Angeles class submarine at over 15 knots (28 km/h) when surfaced and over 25 knots (46 km/h) while submerged.
Design and operational support for the S6G is provided by Knolls Atomic Power Laboratory (KAPL). The S6G reactor plant was originally designed to use the D1G-2 core, similar to the D2G reactor used on the Bainbridge class guided missile cruiser, which is rated at 148 MW. All Los Angeles class submarines from USS Providence (SSN-719) on were built with a D2W core rated at 165 MW, as opposed to the older 150 MW cores found on older boats. The D1G-2 cores are being replaced with D2W cores when the boats are refueled.