NRP Arpao (S161) is an active-service diesel-electric attack submarine of the modern Portuguese Navy. Her keel was laid down in 2005 and the vessel formally commissioned for service on December 22nd, 2010. Her design stems from the German-originated Type 214 design generated by Howaldtswerke-Deutsche Werft GmbH which has since also been adopted by the governments of South Korea and Greece. For the Portuguese Navy, Arpao makes up the second of the two-strong Tridente-class of fighting boats which originally was to number three (one of the vessels eventually cancelled). Her sister ship (and lead of the class) is NRP Tridente (S160). The Tridente-class officially superseded the outgoing Albacora-class.
NRP Arpao takes on a conventional submarine shape by modern standards and is a relatively compact form when compared to the massive American and Russian nuclear-powered designs seen today. She features a flat top deck with her sail mounted amidships. Her forward and aft sections are capped by tapered ends for a fine, streamlined approach. Dive planes are fitted ahead of the sail along the upper hull sides and the powerplant is situated at the rear with the propeller system and rudder arrangement. All told, she displaces at 1,700 tons when surfaced and 2,000 tons when submerged. Her listed length is 222 feet with a beam measuring 21 feet and a draught of 22 feet. Her navigation suite is assisted by a Kelvin Hughes KH-1007 series radar system. Her crew is made up of up to 33 personnel consisting of officers and enlisted sailors.
Power to the Arpao is served from a diesel-electric arrangement comprised of 2 x Siemens Sinavy generators with 2 x MTU 16V396 TB-94 diesel-electric generators and 1 x Siemens Permasyn electric engines driving 1 x propeller shaft. The batteries serve the vessel when submerged and the integrated generators supply propulsion power when the vessel is surfaced. When surfaced, the batteries are charged. The propulsion package is coupled to a low-noise propeller arrangement which provides greater stealth capabilities. Maximum submerged speed is 20 knots with a surfaced speed of up to 10 knots and operational range reached approximately 12,000 nautical miles when running at an 8 knot speed in ideal conditions. The offers the vessel an endurance window of up to 45 days or so. She features a maximum stated depth capability down to 985 feet (300 meters).
As an attack submarine, Arpao is appropriately armed with no fewer than eight 533mm torpedo tubes. She carries a reload stock of twelve Alenia Marconi IF-21 "Blackshark" torpedoes. She may also fire the McDonnell Douglas/Boeing UGM-84 "Harpoon" anti-ship missile and can carry up to six of these missile types. Her Combat Management System (CMS) is headed by the Atlas Elektronik ISUS 90 series suite.
As it stands, NRP Arpao and her sister form a vital component to the modest Portuguese Navy. The Navy also includes frigates, corvettes and patrol boats to help cover the spanning Portuguese coast facing the Atlantic - as well as her national interests further out.
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