O 21-class submarine
# O 21-class submarine

The O 21 class was a class of seven submarines, built for the Royal Netherlands Navy. The boats were still incomplete at the start of the German invasion of the Netherlands O 21, O 22, O 23 and O 24 were hastily launched and escaped to the United Kingdom. O 25, O 26 and O 27 were not able to escape and were captured by the German forces. The Kriegsmarine ordered the completion of the boats and they entered German service as UD-3, UD-4 and UD-5. The submarines' diving depth was 100 meters (330 ft).

## Design

One of the requirements the Royal Netherlands Navy set for the O 21-class was that it had to be able to dive 20 m (66 ft) deeper than the previous class, which was the O 19-class submarine.

## Construction

The ships were built by three different shipyards. O 21 and O 22 were built by the Koninklijke Maatschappij. O 23, O 24, O 26 and O 27 by R.D.M, Rotterdam and O 25 also in Rotterdam at Fijenoord shipyard.

| Name | Laid down | Launched | Commissioned | Decommissioned |
| - | - | - | - | - |
| O 21 | 20 November 1937 | 21 October 1939 | 10 May 1940 (uncompleted) | 2 November 1957 |
| O 22 | 20 November 1937 | 20 January 1940 | 10 May 1940 (uncompleted) | 8 November 1940 |
| O 23 | 12 October 1937 | 5 December 1939 | 13 May 1940 (uncompleted) | 1 December 1948 |
| O 24 | 12 November 1937 | 18 March 1940 | 13 May 1940 (uncompleted) | 22 February 1954 |
| O 25 Commissioned as: UD-3 | 10 April 1939 | 1 May 1940 | 8 June 1941 | 13 October 1944 3 May 1945 (scuttled) |
| O 26 Commissioned as: UD-4 | 20 April 1939 | 23 November 1940 | 28 January 1941 | 3 May 1945 (scuttled) |
| O 27 Commissioned as: UD-5 | 3 August 1939 | 26 September 1941 | 30 January 1942 13 July 1945 (Dutch navy) | 14 November 1959 |
