The S4G reactor is a naval reactor used by the United States Navy to provide electricity generation and propulsion on warships. The S4G designation stands for: * S = Submarine platform * 4 = Fourth generation core designed by the contractor * G = General Electric was the contracted designer This nuclear reactor is the shipboard equivalent of the S3G reactor. It was installed in a dual-configuration on the USS Triton (SSRN-586) with two reactors and two five-blade propellers, which was the first ship to make a submerged circumnavigation of the world.