High Quality Content by WIKIPEDIA articles! HMS Otus (S18) was a Royal Navy Oberon-class submarine. Built in 1962 at Scotts Yard in Greenock, Scotland, the sub`s trials were conducted in Scottish waters, mainly Loch Long and Loch Fyne. Her pennant number (S18) was carried in white paint on the ship`s conning tower fin, however this was removed in 1964 as a discontinued practice.