About 4 pounds of uranium fuel produces more energy than 10 million gallons of fuel oil. Some submarines run on diesel engines. However, the U.S. Navy has not built a diesel-powered submarine since 1959. Diesel engines burn fuel oil and need air for combustion. A submarine can use these engines only when on or near the surface.
Electric batteries supply power underwater.
The snorkel drew air into the submarine when the craft was near the surface. This air replaced oxygen used up by the diesel engines and crew. But the snorkel left a trail through the water and could reveal the submarine's location. Submarines did not become true underwater ships until the development of nuclear power. How a submarine operates Surface operations .