What type of submarine propulsion uses a fuel cell to generate electricity without burning fuel in an engine?

The submarine propulsion method that uses a fuel cell to generate electricity without burning fuel in an engine is air-independent propulsion, commonly abbreviated AIP. It allows a conventional submarine to remain submerged longer than a standard battery-powered boat.

Fuel-cell AIP systems combine hydrogen and oxygen electrochemically to produce electricity, with water and heat as principal by-products. Because the process does not require combustion air, it can operate underwater without a snorkel for extended periods.

AIP does not mean unlimited underwater endurance. Submarines still need stored reactants, batteries, maintenance, and provisions. Nuclear propulsion remains better suited to very long submerged patrols because a reactor can generate power for years without atmospheric oxygen.

Other AIP approaches include closed-cycle engines and Stirling engines. These systems are particularly associated with non-nuclear submarines designed for quiet coastal and regional operations.