1924 - 1945: Oberon Class
Overseas Patrol Submarines
The first submarines to be designed after the First World War were the Oberon Class - a post-war concept of an Overseas Patrol Submarine. With this class it appears that the Admiralty finally decided that the submarine deserved the dignity of a name; thus, the pioneer of the class was called Oberon.
The L Class submarines were chosen as a model for the Oberon design, but the new class had much greater endurance, increased diving depth, improved torpedo armament and increased wireless range. However, a 75 per cent increase in displacement led to a loss of speed, surface and submerged.
During the building of Oberon, the unforeseen growth in topside fittings had a devastating effect on submerged speed and, although modifications were made after her completion in August 1927, a quoted underwater speed of 9 knots, attained from two twin-armature motors developing 1300 bhp, seems impossible.
The two Admiralty-designed six-cylinder diesels in Oberon developed 2700 bhp and, giving a quoted surface speed of 13.75 knots were made at Chatham. Laid down after Oberon, Oxley and Otway were built by Vickers for the Royal Australian Navy and had their engines redesigned, an increase in the bore and stroke of the cylinders giving 3000 bhp, which resulted in an increase in surface speed of approximately 1.5 knots.
Oberon was the first submarine to carry ASDIC - a device originally designed under the auspices of the Allied Submarine Detection Investigation Committee to detect submarines. However, ASDIC, the forerunner of SONAR, was put to good use by submariners against surface targets and took over from the hydrophone which was unable to measure, with any accuracy, the speed, course or distance of an enemy vessel.
On their delivery voyage to Australia in 1928, Oxley and Otwayencountered very severe weather in the Bay of Biscay which badly strained their engine columns, forcing them to remain in Malta for several months whilst British experts repaired the damage. After useful service in the Royal Australian Navy, the two vessels were transferred to the Royal Navy in 1931.
In the Overseas Patrol Submarines practically the whole of the fuel was carried in external tanks. The tanks were riveted and tested to 20 lb/in2, but they leaked to such an extent that they could be considered a failure. Various reasons, such as defective plating, manhole covers and bad equalising arrangements, were blamed for the leaks, and many fruitless attempts were made to overcome the faults. In fact the trouble throughout had been caused by the rivets and, in an era when welded ship construction was in its infancy, the externals were ultimately successfully rebuilt in welded construction.
Of the 19 Overseas Patrol Submarines built, 18 served in the Second World War; 12 of which were lost on active service. The last submarine of this type to be taken out of service was the Vickers-built Otus, in April 1946.