HMS Seadog (P216)
|Builder:||Cammell Laird & Co Limited, Birkenhead|
|Laid down:||31 December 1940|
|Launched:||11 June 1942|
|Commissioned:||24 September 1942|
|Fate:||sold 24 December 1947, broken up August 1948|
|Class and type:||S-class submarine|
|Length:||217 ft (66 m)|
|Beam:||23 ft 6 in (7.16 m)|
|Draught:||11 ft (3.4 m)|
|Complement:||48 officers and men|
HMS Seadog was an S-class submarine of the Royal Navy, and part of the Third Group built of that class. She was built by Cammell Laird & Co Limited, Birkenhead and launched on 11 June 1942. She previously had the pennant P216. So far she has been the only ship of the Royal Navy to bear the name Seadog.
She spent most of her wartime career in the Far East, except for a brief spell in home waters off the Scandinavian coast, where she on 28 December 1943 sank the German transport ship Oldenburg, an ex passenger ship from the Hamburg – Amerika Linie ( HAPAG ).  She was reassigned to the Pacific in early 1945. En route, she rescued three US airmen from a raft in the Bay of Bengal, and shortly afterwards discovered and rescued another. Seadog rendezvoused with an RAF Catalina to transfer these survivors. Upon arrival to the eastern station, she went on to sink six Japanese sailing vessels and a coaster. She later fell in with her sister boat, HMS Shalimar, and together sank another coaster and a tug and a barge.
She survived the Second World War, and was sold on 24 December 1947. She was broken up at Troon in August 1948.
- Colledge, J. J.; Warlow, Ben (2006) . Ships of the Royal Navy: The Complete Record of all Fighting Ships of the Royal Navy (Rev. ed.). London: Chatham Publishing. ISBN 978-1-86176-281-8. OCLC 67375475.