Navy

Cheap, Stealth and Insanely Dangerous: 'AIP' Submarines are Real Killers

One of the most crucial improvements in submarines of the postwar era is the air independent propulsion (AIP) system. First fielded in the 1990s, the development of AIP changed the ways non-nuclear submarines operated, allowing them to fight—and hide—underwater longer. Combined with their extreme quietness, the use of AIP has made modern diesel-electric subs efficient killers, capable of stalking and sinking their prey even in a challenging anti-submarine warfare environment.

Conventional, non-nuclear propulsion submarines previously spent a great deal of time on the surface. Equipped with diesel-electric engines, these submarines needed surface air to run the engines and recharge their batteries. This had the unfortunate effect of limiting the amount of time a submarine could spend submerged, and meant diesel-electric subs would typically leave port sailing on the surface and then submerge once in the patrol area. A reliance on surface air also limited the amount of time a sub could stay underwater during combat.

AIP, while not granting a diesel-electric submarine the same underwater staying power as a nuclear-powered submarine, is still a radical improvement. There are several types of AIP propulsion systems. The Sterling system is one of the oldest, closed-circuit diesel generators, followed by chemical fuel cells. The latest trend in AIP systems is the use of powerful, long-lasting lithium ion batteries.