HMS Unseen
Two submarines of the Royal Navy have been named HMS Unseen

  was a Second World War U-class submarine launched on 16 April 1942 and later served in the Mediterranean, being broken up in 1949.
  is the old name of HMCS Victoria, a long-range hunter-killer (SSK) submarine of the Royal Canadian Navy, that was purchased from the Royal Navy in 1998. See also
 H.M.S. Unseen (novel), a novel by Patrick Robinson

References
 

Royal Navy ship names