Technically, you mean the only USN SSN with two shafts, but even that is incorrect. Nautilus was a conventionally-driven submarine with counter-rotating screws just like its diesel-electric WWII-era forebears.
The first single-shaft U.S. submarine was a diesel research vessel, USS Albacore, which proved the feasibility of many innovations which were later ported over to the nuclear submarine fleet. USS Skipjack was the first nuclear submarine to include most of those features, including single-screw design.
The first single-shaft U.S. submarine was a diesel research vessel, USS Albacore, which proved the feasibility of many innovations which were later ported over to the nuclear submarine fleet. USS Skipjack was the first nuclear submarine to include most of those features, including single-screw design.