Originally Posted by codprawn
They use compressed air to power torpedos!!!
Uhh, no they don't. They expel the fish from the tube with compressed air, but the prop is driven from a small turbine engine (I think.)
Later research on my part shows that there are a number of propulsion systems in use now; ranging from piston engines (US Mk48) to chemical engines (US Mk50 - uses sulphur sprayed onto lithium to generate heat for a steam turbine), to an Ottofuel powered gas turbine (US Mk46, UK Spearfish.) Probably a bunch of battery powered fish, as well.