Home' Defence Technology Review : DTR JUN 2015 Contents 41
DEFENCE TECHNOLOGY REVIEW | ISSUE 10 | JUN 2015
DTR looks at the Swedish
development and international
uptake of air independent propulsion
for diesel-electric submarines.
THE SWEDISH STIRLING development started more than 50
years ago. The first submarine Stirling engine (V4-275R Mk I)
was developed during the late 1970s and underwent extensive
qualification testing between 1983 and 1986, which included
a complete Stirling air independent propulsion (AIP) system
installed and operated in a submarine hull test section.
The Royal Swedish Navy (RSwN) was the first navy in the world
to introduce AIP when an operational prototype was installed
in the A14S submarine Näcken in 1988. After an extensive test
period throughout the following year, HMS Näcken became the
first operational submarine in the world to be fitted with AIP.
A few years later, having gained additional operational
experience from air independent submarine operations, the
Stirling AIP system was incorporated into the new submarine
HMS Gotland, with a class of three submarines commissioned
during between 1996 and 1998.
Further development of the system took place after which the
Stirling AIP system (Mark III) was installed on two additional
Swedish submarines as part of the mid-life upgrade program for
the A17S Södermanland-class in 2004.
Indeed, the incorporation of Stirling AIP systems on all RSwN
submarines is perhaps testament to the capability and reliability
of the system.
The performance and capability of the Stirling AIP submarines
of the RSwN has been excellent. This has been demonstrated
both during national missions and international exercises. The
US and Swedish joint exercises outside San Diego which took
place during a two year period (2005-2006) demonstrated the
value and capability of a diesel-electric submarine equipped with
the Stirling AIP system. The Gotland-class submarine showed
consistent performance during these US west coast exercises,
operating so far away from home port.
Extensive operational testing to verify the reliability and
performance of the Saab Kockums Stirling AIP system has also
been carried out in Japan. In the late 1990s one operational
submarine of the Japan Maritime Self Defense Force (JMSDF)
THE JMSDF HAS SINCE
ENGINES INTO ITS LATEST
LARGE OCEAN GOING
SUBMARINES, THE SORYU
CLASS, AND WILL OPERATE
UP TO 10 SUBMARINES
WITH THIS AIP SYSTEM.
ABOVE: Compact, self-contained and cost-effective to operate
and support, the Stirling AIP system is in service with three navies.
Images: Saab Kockums
AIP TECHNOLOGY EXPLAINED
The AIP system is based on the Stirling engine principle: i.e it is
a heat engine which burns the fuel with oxygen in a continuous
burning flame. The heat from the flame is collected by a working
gas (helium) in the engine and transported to the hot side of the
engine cylinders. By cooling the gas on the opposite side of the
pistons a pressure difference is created which makes the pistons
move and the mechanical movement is converted into electrical
energy. The continuous burning process in combination with
the well balanced system results in very low noise and vibration
levels. The engine itself is housed in an integrated module which
contains noise insulation, cooling, control system and fire
Typically, two to six Stirling AIP modules are integrated
into a submarine, depending on the size of the submarine and
the operational profile. This, together with the self-supporting
modular design, allows for a high level of redundancy.
The Stirling engines are renowned for ease of maintenance
was fitted with a Stirling AIP hull section, similar to the
earlier operational testing undertaken as part of the Swedish
development and testing program.
The JMSDF has since incorporated the Stirling engines
into its latest large ocean going submarines, the Soryu class,
and will operate up to 10 submarines with this AIP system.
The technology transfer and co-operation between Sweden
and Japan has been deep, extensive and successful. In recent
years manufacturing of the Stirling engines for the Japanese
submarines has been made domestically by Kawasaki Heavy
Industries, under a technology licensing arrangement with
The Republic of Singapore Nav y also operates two Archer-
class submarines equipped with the Stirling AIP system.
The Archer class submarine is a modernised version of the
Swedish A17S class with an AIP hull section insertion. The
lead boat in the class, RSS Archer was commissioned in 2012,
with sister ship RSS Swordfish following in 2013.
BELOW: All three submarines of the Gotland-class (HMS
Gotland shown) received the Stirling AIP system during their
construction in the mid-late 1990s.
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