A hydrogen generation apparatus for an underwater vehicle is presented, the apparatus including a hydrolysis reaction compartment, a mass of solid lithium hydride disposed in the compartment, inlet and outlet structure for passing sea water through the compartment to generate steam, lithium hydroxide and hydrogen gas, a condenser for condensing out the steam and retaining the condensate and lithium hydroxide, and a tank for collecting the hydrogen gas, the tank having outlet structure for discharging the hydrogen gas to a vehicle propulsion system.