The Dolfijn-class submarines of the Royal Netherlands Navy are a class of four submarines; Dolfijn, Zeehond, Potvis and Tonijn. They were built in the late 1950s and the early 1960s. They were the first indigenous submarines built in the Netherlands and for the Royal Netherlands Navy after World War II. In the Netherlands they are also known as "three cylinder" submarines. They formed the backbone of the Royal Netherlands Navy Submarine Service during most of the Cold War.