HNLMS Tonijn (Dutch: Thunnus) was a Potvis-class submarine (modified Dolfijn class) of the Royal Netherlands Navy.

The submarine was laid down on 26 October 1962 at the Wilton-Fijenoord shipyard in Schiedam and launched on 14 June 1965.

[3] While on exercise northwest of Ireland, she received the news that the US Navy's submarine Walrus had gone missing.

[3] From 18 to 28 July 1976 Tonijn made a visit to Kiel to participate in the Kieler Woche.

[3] In 1984 the boat participated in an exercise at Zeebrugge with HNLMS Van Speijk and the Wielingen.