HMS Seahorse was a first-group S-class submarine of the Royal Navy, built at Chatham Dockyard. She was ordered in 1931, laid down on 14 September 1931, launched on 15 November 1932, and commissioned on 2 October 1933. Her pennant number was 98S (S 98).
Early Career
Before the Second World War, Seahorse served as part of Britain's growing submarine force. In September 1938 she was damaged in a collision with the destroyer HMS Foxhound but was repaired and returned to service.
At the outbreak of war in September 1939, HMS Seahorse joined the 2nd Submarine Flotilla and began patrols in the North Sea and off the Norwegian coast.
Wartime Operations
During her first war patrol southwest of Stavanger, Norway, the patrol itself was uneventful. However, while returning to base she was mistakenly attacked with depth charges by a British aircraft, suffering damage that required repairs.
On later patrols she encountered German naval forces several times:
- On 13 November 1939 she sighted the German submarine U-36 and fired torpedoes, but missed.
- During another patrol she sighted U-21, but the German submarine submerged before an attack could be launched.
- On 18 November 1939 she observed two German destroyers, believed to be Z21 Wilhelm Heidkamp and Z19 Hermann Künne, but could not manoeuvre into a firing position.
Although she made several contacts with the enemy, Seahorse achieved no confirmed sinkings.
Final Patrol
On 26 December 1939, under the command of Lieutenant Dennis Staunton Massy-Dawson, HMS Seahorse departed for her sixth war patrol. She was ordered to patrol off Heligoland, later moving to the mouth of the River Elbe, before returning on 9 January 1940.
She never returned.
For many years it was believed that she had struck a mine. Later examination of German records suggested a different fate. On 6-7 January 1940, vessels of the German 1st Minesweeping Flotilla detected and repeatedly depth-charged an unidentified submarine northwest of Heligoland. Many historians now believe this submarine was HMS Seahorse.
Legacy
HMS Seahorse was one of the earliest Royal Navy submarine losses of the Second World War. Unlike HMS Starfish and HMS Undine, whose crews survived to become prisoners of war, Seahorse disappeared with all hands and left no survivors to tell her story.
Key Facts
- Pennant Number: 98S (S 98)
- Class: S-class submarine
- Builder: Chatham Dockyard
- Commissioned: 2 October 1933
- Commanding Officer at loss: Lt Dennis Staunton Massy-Dawson
- Lost: During her final patrol, January 1940
- Probable Cause: Depth-charge attack by the German 1st Minesweeping Flotilla near Heligoland.
