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Dolfijn / Potvis

The Dolfijn class submarines of the Royal Netherlands Navy were the first indegenous submarines built for the Netherlands Navy after World War II. Dolfijn and Potvis are officially considered to be a separate class, the Dolfijn class consisting of Dolfijn (3) / Zeehond (3) and the Potvis class consisting of Potvis / Tonijn. These boats had their diesels replaced and electronics updated in 1978-79. All four boats are almost identical after modernization. The order for the second group of boats, the Potvis class, was postponed in the late 1950's while the possibility of building a nuclear powered submarine was considered and rejected. The order for two boats was re-instated in 1962.

The ship was equipped with two M.A.N. 6V6 diesel engines of 1550 PS each. In a later units they were replaced by 2200 PS motors.

The RHMS "Tonijn" ("Tuna" - Dutch submarines are often named after fish) had been designed by engineer M. F. Gunning. Tonijn was constructed between 1962 and 1965 in Schiedam, The Netherlands. On 24 February 1966 commander J.J. Vaessen received the command over the "Tonijn" and it's 67 crew members. The submarine "Tonijn" was demobilised in 1991. Since 1993 it is displayed on land next to the maritime museum in Den Helder, The Netherlands.

The boat is an example of the so called Three-Cylinder construction method. The pressure hull is formed by three cylinders, which were connected by access shafts. The disadvantage of this construction method was a forced separation of all functions of the ship between three separated cylinders. This required extensive machinery and a larger crew. The design also made for much improved stability. The top cylinder forms the living/work quarters of the crew and the bottom two cylinders house the engines, batteries and storage rooms. Due to better welding techniques and advanced materials, later Dutch boats are monohull.