100 YEARS OF BARROW-BUILT RN SUBMARINES, 1901-2001
OVERSEAS PATROL, 1925-1946
The first submarines to be designed after the First World War. were the O 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 L50 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, both 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 only 9 knots, attained from two twin-armature motors developing 1300 bhp, is hard to believe.
The two Admiralty-designed six-cylinder diesels in Oberon made at Chatham developed 2700 bhp and gave a quoted surface speed of 13.75 knots. Laid down after the Oberon, Oxley and Otway were built by Vickers for the Royal Australian Navy but 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 Otway encountered 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 1925, the need for a new programme of Overseas Patrol Submarine construction resulted in the Odin Class. This class was 13 feet longer than the Oberons, owing, primarily, to a 7ft 6in increase in the engine room length. Odin was approved by the Board in August 1926, and was the first of a class of six: the others being Oswald; Osiris; Otus; Olympus and Orpheus.
In the 1927 Programme, six Parthian Class submarines were ordered (Parthian; Perseus; Poseidon; Proteus; Pandora and Phoenix), and in the following year six Rainbow Class (Rainbow; Regent; Regulus; Rover; Rupert and Royalist) were also ordered. Of the latter, Rupert and Royalist were subsequently cancelled. Although slightly larger than the O boats, the main particulars of these two classes were practically the same. But, in an attempt to make living conditions more pleasant on long surface passages to the Far East, the Rainbow Class were fitted with a galley on the upper deck and a shower in the conning tower.
The Odin, Parthian and Rainbow Classes were all fitted with four-cycle blast-injection eight-cylinder diesels, accommodated in the larger engine room and designed to develop a total of 4400bhp in the Odins and 4640 bhp in the Parthians and Rainbows. In each case, the main engines were made by the building Yard.
By the late 1920s, the ability to dive quickly had become a major consideration but it was believed that a submarine could not submerge faster than about two feet per second. The minimum time to dive from full buoyancy to periscope depth appears to have been of the order of one minute. The range of sea-water density in which submarines of the period were designed to dive was quite limited, and it wasn't until late in the building of the Odin Class that a requirement to be able to dive in fresh water was introduced - resulting in changes to the compensating water tanks. The ability to dive in waters with a specific gravity of 1.00 to 1.30 remained for all submarines until the Second World War, after which it decreased to 1.015 to. 1.03.
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.
MAIN PARTICULARS Oberon Class Oxley & Otway Odin Class Parthian Class Rainbow Class
Classes
Length overall 269ft 8 in 275ft 283ft 6in 289ft 2 in 287ft 2in
Beam 27ft 11 1/2 in 27ft 7 5/8 in 29ft 10 3/4 in 29ft 10 3/4 in 29ft 11 in
Depth, pressure hull 16ft 8 5/8 in 16ft 7 1/2 in 16ft 11 7/8 in 16ft 11 3/4 in 16ft 11 7/8 in
