HMS Oberon (P21)

HMS Oberon was the prototype for the Odin-class submarine of the Royal Navy.

Design
Oberon was the prototype for the Odin-class submarines and was initially named O1 but renamed in 1924, becoming the first named British submarine. Ordered under the 1923 programme, she was the fifth ship of the Royal Navy to carry the name Oberon. The submarine was built in response to the demise of the Anglo-Japanese Alliance in 1922, which necessitated a need for a long-range patrol submarine capable of operations in the Far East. Oberon differed from the predecessor L-class submarines in that she was lengthened by 32 ft and broadened by 3 ft, in addition to a two-knot reduction in top speed, expanded range, and double the number of torpedoes and torpedo tubes.

With a complement of 54, Oberon was 270 ft long overall with a beam of 28 ft and a draught of 15.5 ft. She displaced 1311 LT standard and 1598 LT normal while surfaced, but displaced 1831 LT normal while submerged. The submarine was propelled while surfaced by two Admiralty diesel engines rated at 2950 bhp and by two electric motors rated at 1350 shp, each driving one propeller shaft. These gave her a maximum speed of 13.75 kn surface and 7.5 kn submerged – both short of a planned 15 kn surfaced and 9 kn submerged.

The submarine had a pressure hull with 3/4 in-thick plating, to which saddle tanks were fitted, allowing for a maximum design depth of 500 ft, though Oberon was only tested to a depth of 200 ft. She was capable of carrying 186 lt of oil, mostly in leakage-prone external tanks riveted to the hull, which were replaced by welded tanks in a 1937 refit.

Initially armed with a single QF 4 inch/40 naval gun Mk IV (replaced with the Mk XII in the 1930s) for surface fighting, Oberon had eight 533 mm torpedo tubes – six bow and two in the stern. The submarine could carry sixteen torpedoes, originally Mark IV but later replaced by Mark VIII. Oberon was the first submarine of the Royal Navy equipped with asdic while under construction, and was additionally equipped with Type 709 hydrophones and a Type SF direction finder. Modifications made during the Second World War included the addition of an Oerlikon 20 mm cannon for anti-aircraft defense and a Type 291W radio direction finder for air and surface warning.

Construction and service
She was laid down on 22 March 1924, launched on 24 September 1926 at the Chatham Dockyard and commissioned on 24 August 1927. As a result of torsional vibration in her powerplant, the submarine was never deployed to the Far East. Oberon was stationed at Portsmouth between 1927 and 1931, then moved to the Mediterranean before returning to Portsmouth in 1934. On 11 October 1935, she collided with the destroyer HMS Thanet (H29) at Devonport. Placed in reserve in 1937, Oberon was recommissioned on 2 August 1939 and was used for training during the Second World War. Lieutenant Michael Lindsay Coulton Crawford, previously commander of HMS Unseen (P51) in the Mediterranean, was given command on 24 March. She was decommissioned at Blyth on 5 July 1944 and was sold for scrap on 24 August 1945. Oberon was scrapped at Dunston by Clayton and Davie.

She was assigned a pennant number of 21.P, which was changed to 21.N in 1939 and to N.21 in 1940.