Walrus-class submarine

The Walrus-class submarine is the only submarine class currently in operation in the Royal Netherlands Navy. They have been in service since 1990 and are all named after sea mammals.

Design
The Walrus-class submarines are unusual in that instead of a cross-shaped assembly of stern diving planes and rudders, they mount four combined rudders and diving planes in an "X" configuration. This tail configuration was first tested in 1960 on the United States Navy's USS Albacore (AGSS-569), but has since been used only by the Walrus class, all Swedish Navy submarines since the Sjöormen class, the Royal Australian Navy's Collins class and the German Type 212A.

The submarines were in high demand by NATO during the Cold War since they combined a highly skilled crew with a very silent boat. At that time the majority of NATO submarines were either nuclear or brown water subs, with the Walrus class being among the rare blue water diesel electric submarines in service.

Operational History
After the Cold War, the subs have been tasked for many intelligence gathering operations (still classified) in the Yugoslavian region, Iraq and the Caribbean.

In June 2010, the Netherlands agreed to deploy one submarine to help combat piracy in the waters off Somalia. Possible missions could include signals intelligence, e.g. going close to shore and intercepting pirates' radio signals, and tracking of pirate vessels.

Upkeep program
In 2007, the cabinet approved an upgrade of the four operational vessels and recruitment of additional crew to improve overall operational availability. The upgrades are focused on near-shore operations and integration with new weapons. These include the US migration from the current MK 48 mod-4 torpedo to the mod-7 version, replacing one periscope with an non-hull-penetrating optronic mast from L-3 KEO which enables the submarine to capture HD footage both day and night, addition of a Mine & Obstacle Avoidance Sonar by Kongsberg, refurbishing of the pressure hull and introduction of a new combat management system.

Boats
All boats were built by the Rotterdamsche Droogdok Maatschappij.

General characteristics

 * Displacement: 2,350 t surfaced, 2,650 t submerged, 1,900 t standard
 * Dimensions: 67.73 x 8.4 x 6.6 m
 * Propulsion: 3 SEMT Pielstick diesels, 1 Holec mainmotor, 1 shaft, 6 blades
 * Speed: 13 knots surfaced, 20 knots submerged
 * Complement: 50 to 55
 * Surface Search Radar: DECCA 1229
 * Sonar Systems: Thomson Sintra TSM 2272 Eledone Octopus, GEC Avionics Type 2026 towed array, Thomson Sintra DUUX 5B passive ranging and intercept
 * Fire Control: HSA SEWACO VIII action data automation, GTHW integrated Harpoon and torpedo FCS
 * Armament: 4 x 21 inch (533mm) torpedo tubes (20 Honeywell Mk 48 or Honeywell NT 37 torpedoes, mines, SubHarpoon SSM)