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.