Q HISTORY
THE ROYAL NAVY’S LAST FLEET SUBMARINES
Words: Keith Ray
30 A
‘fleet submarine’ was one designed to accompany capital ships on the surface, and then pull ahead when required and submerge to attack enemy vessels ahead of the fleet. By definition the
fleet submarine had to be capable of at least the same speed as the fleet itself, and as warships increasingly used geared steam turbines they became significantly faster. This was becoming something of an issue
by the late 1920s when, for example, the Nelson Class of battleship introduced in 1927 could sustain 23 knots. However, the concept of a fleet submarine
was still active in 1928 when the disastrous K-Class submarines were removed from service. The K-Class certainly had ‘fleet’ speed in its day, capable of 24 knots on the surface, but the steam power plant proved to be a significant problem when it came to submerging. The order for the last four K-Class vessels was cancelled once it was finally realised the design was doomed, and the order was replaced by one for four M-Class vessels, of which three were completed.
These were basically K-Class hulls with
diesel power replacing steam, giving a lower top surface speed of 15 knots. Like the K-Class, the M-Class with their massive 12-inch guns were far from a success, having, among other drawbacks, to fully surface to reload the gun. Even though it was clear the diesel engines
of the day were not capable of propelling a submarine at the speed of Royal Navy warships, the Admiralty still demanded ‘submarines which, in an ocean war, should be capable of operating within the fleet’, and it was this unrealistic request that led to the development of the River Class fleet submarine. The plans were submitted to the Board of
the Admiralty in June 1929, and it was originally going to be a class of 20 vessels, but in the end a change of policy resulted in the class being reduced to just three, HMS Thames, HMS Clyde and HMS Severn, all built by Vickers at Barrow-in-Furness, Cumbria, in the north-west of England. The first of the class, Thames, was slightly
smaller than her two sister vessels, both of which incorporated a number of improvements from the many lessons that were learned during the construction of Thames.
Each vessel cost around £500,000,
equivalent to just under £30 million in today’s money. They were large and, it is reported, fairly comfortable by submarine standards. The class was of a fairly conventional
design, long and well streamlined, and without the large guns that the M-Class had carried. The design called for a surface speed of 22.5
knots, which whilst it made them the fastest submarines in the Royal Navy at the time, was slightly less than the top speed of the Nelson Class battleships introduced in 1927, and also less than the older K-Class steamers. In any case the development of geared steam turbines, first used for battleships in the Revenge Class of 1916, promised even faster capital ships, so the decision to build the River Class vessels appears rather flawed from the outset. In fact, although specifically designed for the role, none of the three submarines in the class ever actually operated as a ‘fleet’ vessel. The requirement for ‘fleet speed’ called for considerable power when operating on the surface. Surface power for the River Class came from two 10-cylinder four-stroke blast- injection diesel units of Admiralty design, producing 8,000 bhp at 400 rpm. Two auxiliary
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