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. 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. After the Cold War, the subs have been tasked for many highly confidential intelligence gathering operations (still classified) in the Yugoslavian region, Iran, Iraq and the Caribbean often on request of Allies, including NATO and the United States. In 2007, the Dutch cabinet approved an upgrade of the four operational vessels and recruitment of additional crew to improve overall operational availability. The upgrades were focused on near-shore operations and integration with new weapons,and include: the migration from the then current MK 48 mod-4 torpedo to the mod-7 version, replacing one periscope with a 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 ELAC Nautik, refurbishing of the pressure hull and introduction of a new combat management system In November 2014 the Dutch Minister of Defence announced plans to replace the Walrus-class submarines in 2025. In November 2016, the Russian Navy claimed to have chased off a Walrus-class vessel from a battle group that included the Admiral Kuznetsov.