The 'O' class (later 'Oberon' class) was developed as a replacement for the ocean-going 'L' class of World War I design. They were categorized as overseas patrol submarines, and it is of interest to note that, even as early as the concept stage in 1922, there was a requirement for long range with an eye to possible future operations against Japan (an ally during 1914-8). The lead boat, HMS Oberon, was laid down by Chatham Dockyard in 1924 and was closely followed by two sisters, HMS Otway and Oxley. Six bow and two stern tubes were fitted, with a reload for each. These, together with extensive bunker spaces, made for a large hull which proved distinctly unhandy, with speed reduced by a plethora of external fittings. Even after much fairing and attention they barely achieved their designed surface speed, and failed altogether to reach the required speed submerged.
The hull was fitted with saddle tanks, which contained most of the ballast capacity. Some could double as extra fuel tanks but were unpopular as they inevitably emitted telltale oil traces through leaky rivet heads. As with the 'L' class boats, a 101.6-mm (4-in) gun was fitted in the tower to allow it to be worked in heavy seas.
Because of the limitations with the 'Obérons', an improved 'Odin' class was evolved: longer to accommodate more powerful machinery and beamier to improve stability in the surfaced condition. Completed in 1928-9, these boats were HMS Odin, Olympus, Orpheus, Osiris, Oswald and Otus. Though still plagued by weeping oil, their outsides were marked by a great clean-up of general clutter. An interesting idea, fortunately not pursued, was to install auxiliary accom modation in the upper casing to ease the confines of the crew on extended patrols. The 'Parthian' and 'Rainbow' classes were essentially 'Odin' repeats; six of each were ordered, differing only in detail. Two 'Rainbows' were ultimately cancelled, and the units completed in 1929-30 were HMS Parthian, Perseus, Phoenix, Poseidon, Proteus, Pandora, Rainbow, Regent, Regulus and Rover.
Most of the O' class boats were in the Far East in September 1939 but one of those in home waters, the Oxley, had the melancholy record of being the first British submarine lost when torpedoed in error by another British submarine, HMS Triton. Of the joint class total of 18, 12 were lost, most by the end of 1940 and many in the Mediterranean, for whose confines they were totally unsuited.
Specification 'Odin' class Displacement: 1,781 tons surfaced and 2,038 tons submerged Dimensions: length 86.41 m (283.5 ft); beam 9.12m (29,92 ft); draught 4.17 m (13.67ft) Propulsion: two diesels delivering 3281. l kW (4,400 bhp) and two electric motors delivering 984.3 kW (1,320 hp) to two shafts Speed: 17.5 kts surfaced and 9 kts submerged Endurance: 21123 km (13,125 miles) at 8 kts surfaced and 97 km (60 miles) at 4 kts submerged Armament: one 101.6-mrn (4-in) gun and eight 533-mm (21-in) torpedo tubes (six bow and two stern) Complement: 53