Laid down in May 1933, and launched in March 1934 the Steel ‘S’ Class submarine HMS Sealion was built by Cammell Laird at Birkenhead (Yard No.989). Her steel hull displaced 980 tons submerged and 780 tons on the surface. She measured 208.7′ x 24.0′ x 10.5′ and she was powered by twin 1550 brake horse power diesel engines for surface operation and twin 1300 horse power electric motors while deep submerged with dual shafts. Her armament included six 21 inch torpedo tubes forward, with a further 6 torpedos for reload purposes, a 3 inch deck gun and a .303 calibre AA machine gun.
At the outbreak of the Second World War, Sealion was based at HMS Maidstone in Malta but was quickly transferred back to the UK where she was moved between bases in Portsmouth, Harwich and Blyth. In the early years of the war she was heavily involved in the struggle with the German Navy in the North Sea and was successful in sinking four ships off the Norwegian coast during 1940 and 1941. Under the command of Lieutenant Commander Benjamin Bryant DSC RN she attacked but failed to sink U-21 off the Dogger Bank in November 1939. She sank the German merchant August Leonhard in April 1940 off the Danish island of Anholt and was then involved in a number of unsuccessful attacks before finishing her patrol by sinking the Norwegian merchant Toran in August. On 5th February 1941 she shelled and sank the Norwegian cargo-passenger ship Ryfylke. On her next patrol in July 1941 she attacked French shipping, sinking the French fishing vessels Gustav Eugene and Gustav Jeanne, and on succeeding days, Christus Regnat and St Pierre d’Alcantara. She was also one of a number of submarines ordered to track the German battleship Bismark in the days preceding her eventual sinking. Finally, towards the end of 1941, now under command of Lieutenant G R Colvin RN, she sank the Norwegian tanker Vesco and the Norwegian merchant Island.
From 1942 – 44, when she was replaced in front line action by more modern vessels, she was used for submarine training exercises before she was scuttled, off the south end of Arran, as an ASDIC target on 3rd March 1945.
The wreck lies two and a half miles south west of Pladda in a general depth of 62 metres in position 55°23.383’N, 005°08.301’W and rises 6 metres from the seabed. She lies approximately 140/320°. The wreck has been snagged by ropes and nets and due to the general poor visibility often encountered, please take care when undertaking a dive on this wreck.
