The Oberon, Odin, Parthian and Rainbow Classes were designed to dive to a depth of 500 feet. The Oberons were tested to 200 feet and in the three later classes the deep diving trials were to 300 feet, although it is known that some boats went deeper. Rear-Admiral Submarines (RA(S)) laid down 300ft as the test diving depth of boats designed to withstand depth pressure at 500 feet.
It is interesting to review the policy regarding deep diving. In 1928, the Director of Tactical Division (DTD) stated that: 'The ability to dive to 500 feet was introduced principally in order that pressure hulls of these submarines should be more capable of withstanding the effect of the explosion of a depth charge. Submarine officers do not visualize any intentional diving to such depths as 500 feet though the ability to do so is an asset in the event of an involuntary deep dive which might cause the submarine to go much deeper than was intended'.
When on patrol, the daily fuel consumption for all classes, allowing 12 hours diving, 12 hours steaming at slow speed and eight hours charging, was given as 2.1 tons per day, except in Orpheus (the only vessel of the Odin Class to be fitted with a Vulcan clutch) where the consumption was 2.6 tons per day.
In the Overseas patrol Submarines, practically all of the fuel was carried in external tanks. The tanks were riveted and tested to 20 lb/in, but they leaked to such an extent that they could be considered a failure. Various reasons, such as defective plating, manhole covers and bad equalizing 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 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.
