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Kockums Stirling AIP System

Air-independent propulsion under water

Kockums Stirling AIP

More than 20 years of operational service

In 1988 Kockums fitted a Stirling engine in the Royal Swedish Navy submarine HMS Näcken to achieve air-idependent propulsion. The submarine was placed in dry-dock and cut in two. A fully outfitted eight-meter Stirling AIP section was then inserted.

The years of practical sea-trials that followed were extremely satis-factory and resulted in the installation of Stirling AIP systems in the new Gotland Class submarines.

Increased submerged endurance

Installation of a Stirling AIP unit. View larger image

Installation of a Stirling AIP unit.

The Kockums Stirling AIP system considerably increases the sub-merged endurance.

The systems offers an alternative to battery power, which in turn means less frequent requirements for noisy battery recharging, with the diesel generators.

Instead of a number of days, a Stirling AIP submarine can extend the time submerged to weeks and thus outperform any other conventional submarine with regard to that key capability - submerged endurance.

Outstanding advantages

Stirling AIP unit onboard a sub. View larger image

Stirling AIP unit onboard a sub.

The main feature of the Kockums air independent propulsion (AIP) system is the use of Stirling engines burning pure oxygen and diesel fuel in a pressurized combustion chamber.

The combustion pressure is higher than the surrounding seawater pressure, thereby allowing the exhaust products, dissolved in seawater, to be discharged overboard without using a compressor.

Oxygen is stored in liquid form (LOX) in cryogenic tanks. Submerged endurance is primarily determined by the amount of stored LOX.

Kockums Stirling AIP system shows important overall advantages:

  • The Stirling AIP system is readily available. It is mature technology, proven in operational service.
  • The Stirling AIP system is practically vibration-free, silent and wakeless. Its infrared signature is very low. 
  • The Stirling AIP system is an add-on system. When the LOX supply is exhausted, the submarine remains a powerful conventional submarine. 
  • The Stirling AIP system has a low acquisition cost and a low life-cycle cost. The necessary infrastructure already exists. 
  • The Stirling AIP system is equally well suited for modernization of existing submarines and for integration into new submarine designs.
The principle of the Stirling AIP system. View larger image

The principle of the Stirling AIP system.

Page updated Thursday, November 19, 2009.

Related information

Submarine brochure (pdf)

At the leading edge of submarine technology

At the leading edge of submarine technology


Stirling AIP in Japan

Kockums Stirling AIP used by Japan.

Kockums has an agreement with Kawasaki Heavy Industry for license production of Stirling engines for the Oyashio class submarines of the Japan Maritime Self Defense Forse (JMSDF).

Read more

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