AIP (Air-Independent Propulsion)

Air-independent propulsion lets a non-nuclear submarine generate power submerged without drawing atmospheric oxygen, extending the dived endurance of an SSK from days to two or three weeks. The three fielded technologies are the Stirling engine burning diesel with stored liquid oxygen (Sweden’s Gotland, Japan’s Soryu), closed-cycle diesel, and the polymer-electrolyte hydrogen fuel cell used in Germany’s Type 212A. AIP yields very low indiscretion rates at patrol speeds but produces only tens to a few hundred kilowatts, so the boat still snorkels its main diesels to recharge for transit and sprint.