The Walrus-class submarine is the only submarine class currently in operation in the Royal Netherlands Navy. The boats have been in service since 1990 and are all named after sea mammals. History In 1974, the Royal Netherlands Navy announced, through the Ministry of Defence's 10-year plan , that it wanted to replace its aging s. Since the 1960s, the Royal Netherlands Navy had been conducting studies and research into a suitable replacement attack submarine. This research initiative concluded that the Netherlands should build conventional diesel-electric submarines, as nuclear submarines were costly and could only be constructed, crewed, and maintained by countries with major navies such as the United States, France and the United Kingdom. Nonetheless, even with the diesel-electric submarine, the Dutch government sought to work together with international allies to reduce construction costs. Between 1975 and 1978, the design of the Walrus-class was for the most part completed, and included many improvements which would result in new, state-of-the-art submarines that would mark a significant improvement over previous submarines used by the Royal Netherlands Navy. For example, a special kind of French-produced steel was used to construct the hull of the Walrus-class submarines; this steel proved to be more elastic, allowing submarines of the class to dive deeper than previous submarines. Furthermore, there was a focus on automation which was aimed at decreasing the manpower required to operate the submarines, while also making them more effective against threats. On 19 June 1979, Minister of Defense Willem Scholten signed a contract worth 425 million guilders with the Rotterdamsche Droogdok Maatschappij (RDM) to build two submarines to replace the Dolfijn-class submarines, with the construction of the second boat to commence the following year. Soon, RDM noticed that the new submarines could not be built the same way as the s; it had to use new techniques to build the submarines. Furthermore, the design was constantly modified to incorporate new developments in the submarine world, which led to issues that slowed the building process. Nonetheless, construction continued and on 11 October 1979, was laid down. Two years later, on 24 September 1981, was laid down. Unexpectedly, on 19 February 1983, RDM's parent company Rijn-Schelde-Verolme declared bankruptcy, despite successive governments providing 2.2 billion guilders in state aid to RSV. This was problematic because the construction of the Walrus-class submarines was far from completion. To ensure construction of the submarines continued, RDM was re-established as