WHMS Oberon was the prototype for the -class submarine of the Royal Navy.
WHMS Odin (N84) was an O-class submarine of the Royal Navy. She was laid down by HM Dockyard at Chatham in Kent on 23 June 1927, launched on 5 May 1928 and commissioned on 21 December 1929. The name Odin refers to the 74-gun, Danish man-of-war surrendered to the British in 1807.
WHMS Olympus was an Odin-class submarine, a class originally designed for the Royal Australian Navy to cope with long distance patrolling in Pacific waters. Olympus was built to the same design for the Royal Navy. She served from 1931 to 1939 on the China Station and 1939-1940 out of Colombo. In 1940 she went to the Mediterranean. She was sunk by a mine off Malta in May 1942. Her last commanding officer was Lt. Commander Herbert George Dymott, who was one of the 89 crew members killed in the sinking.
WHMS Orpheus (N46) was an O-class submarine of the Royal Navy. She was laid down by William Beardmore and Company on the Clyde on 14 April 1927, launched on 26 February 1929 and commissioned on 23 September 1930.
WHMS Oswald was an Odin-class submarine built for the Royal Navy during the 1920s.
WHMS Osiris was an O-class submarine of the Royal Navy. She was laid down by Vickers-Armstrongs of Barrow-in-Furness on 12 May 1927, launched on 19 May 1928 and commissioned on 25 Jan 1929.
WHMS Otus was an O-class submarine of the Royal Navy. She was laid down by Vickers-Armstrongs of Barrow-in-Furness on 31 May 1927, launched on 31 August 1928 and commissioned on 5 July 1929.
WHMS Otway was an Odin-class submarine of the Royal Australian Navy (RAN) and Royal Navy (RN).
WHMS Oxley was an Odin-class submarine of the Royal Australian Navy (RAN) and Royal Navy (RN).