What fuel does a submarine use?

Answer 1

WWII subs burned diesel fuel. Nuclear-powered submarines use uranium in their nuclear reactors. They also have diesel-powered generators, which use diesel fuel.

One of the first military submersibles - called the "Turtle" and invented during the American Civil War - was powered by the single occupant's leg & arm muscles, operating various "propellers" on the exterior of his barrel-shaped device. This was not terribly efficient. Subsequently, early attempts were made to power submersibles with steam engines, underwater oars and more hand-cranking.

None of these methods were particularly successful.

Eventually a chap called John Holland designed perhaps the first true submarine, powered by batteries whilst submerged and by an internal combustion engine whilst on the surface. The i/c engine also charged the main batteries whilst running. This design was improved and modified until German engineers built the Type VII "Unterseeboot" or U-Boat of WW2 fame, which culminated in the Type XXI Diesel-Electric layout used by most D/E boats today.

But that's not all. Modern submarines - even the "Schnorkel"-equipped Diesel electric designs in use today - have several major weaknesses. They have to come up to let their crews breathe fresh air, they need fresh water for drinking and their batteries - and those batteries have to be recharged whilst the submarine is at periscope depth - a particularly risky place to be in a submarine.

So, if you fit a small nuclear reactor into a well-shielded area of a new submarine design, let the heat from that reaction superheat some water, you can generate steam to run a turbine - for propulsion and for electrical power. With this amount of power available, you can keep the internal air clean by splitting seawater into Oxygen and Hydrogen, then scrubbing the exhaled CO2 breathed out by the crew. You can make fresh water from seawater and - basically - a modern nuclear boat doesn't have to surface for months at a time. In fact, the main limit to the time one of these ultimate arbiters of peace stays submerged is the amount of food it carries for its crew.