Gotland-class submarine

The Gotland class submarines of the Swedish Navy are modern diesel-electric submarines, which were designed and built by the Kockums shipyard in Sweden. They are the first submarines in the world to feature a Stirling engine air-independent propulsion (AIP) system, which extends their underwater endurance from a few days to weeks. This capability had previously only been available with nuclear-powered submarines.

Features
As of 2008, the Gotland-class attack submarine is one of the most modern submarines of the Swedish Navy in service, mainly designed for submarine missions such as anti-ship/anti-submarine warfare, collecting of intelligence (communications intelligence (COMINT), electronic signals intelligence (ELINT)), forward surveillance, special operations and mine-laying tasks.

On the water surface, the submarine is powered by two sets of MTU engines. While submerged, the Kockums-built Stirling engine Air Independent Propulsion (AIP) system is used to drive a 75 kW generator for either propulsion or charging the batteries. A Stirling engine is particularly well suited for a submarine because the engine is near silent and can use the surrounding sea water as a heat sink to increase efficiency. Submerged endurance is dependent on the amount of liquid oxygen stored on-board and is described as "weeks". The class is characterized by its low acoustic signatures, extreme shock resistance and a competent combat system.

Kockums touts extreme maneuverability for this class due to the hull design and a well-placed X rudder. The X rudder provides four control surfaces, along with two mounted on the sail, which enables sharp turns and the ability to operate very close to the seabed. Ship automation and computerized steering allow a single operator to steer the submarine in depth and course, which also results in a smaller crew complement, leading to good accommodation standards and low operating costs.

The class has many features that enhance stealth, helping it to remain undetected. All shipboard machinery are isolated and mounted on rubber dampeners to reduce vibrations and noises; a hydrodynamic hull design to reduce noise, infrared signature, and active sonar response; counteracting its magnetic signature with 27 independent electromagnets; short circuiting extremely low frequency (ELF) electrical fields; various hull coatings to reduce active sonar response; and coating the mast with radar absorbing material. Combined with the near silent operation of the Stirling generator and slow turning propeller to prevent cavitation, the boats are very difficult to detect underwater, especially in their normal area of operations, the Baltic Sea.



Deployments
After being refit and upgraded to sustain the higher temperatures of tropical water, HMS Halland took part in a multi-national exercise in the Mediterranean from September 16, 2000. Allegedly, there she remained undetected while still recording many of her friendly adversaries, attracting interest from the participating countries. In early November the same year, she participated in a NATO "blue-water" exercise in the Atlantic. There she reportedly won a victory in a mock "duel" with Spanish naval units, and then the same in similar duel against a French SSN, a nuclear-powered attack submarine. She also "defeated" an American SSN, the USS Houston.

Secondment to United States Navy
In 2004, the Swedish government received a request from the United States of America to lease HMS Gotland – Swedish-flagged, commanded and manned, for a duration of one year for use in anti-submarine warfare exercises. The Swedish government granted this request in October 2004, with both navies signing a memorandum of understanding on March 21, 2005. The lease was extended for another 12 months in 2006. In July 2007, HMS Gotland departed San Diego for Sweden.

HMS Gotland managed to snap several pictures of the USS Ronald Reagan during a wargaming exercise in the Pacific Ocean, effectively "sinking" the aircraft carrier. The exercise was conducted to evaluate the effectiveness of the US Fleet against diesel-electric submarines, which some have noted as severely lacking.

Overhaul
In March 2013, Kockums received an order for an overhaul for two of the Gotland class submarines. The overhaul is expected to be completed by 2017. With these upgrades, the submarines will be able to remain in active duty until after 2025 alongside the new A26 submarines (NGU).