1929 - 1945: River Class
Even though marine diesel engines of the period were incapable of propelling submarines as fast as surface craft, the Admiralty still wished, perhaps misguidedly, to build Fleet Submarines, and continued to discuss, at length, the functions and requirements of such vessels. In 1928, the culmination of the removal from service of the K Class submarines and the demand by Rear Admiral (Submarines) for
submarines which, in an ocean war, should be capable of operating with the Fleet
led to the development of the River Class Fleet Submarine.
Submitted to the Board in June 1929, the River Class were conventional submarines, long, well streamlined and without any large guns or other unusual features. All three vessels of the class were built at Barrow, the first of class Thames completing in September 1931, and her slightly larger sister ships, Severn and Clyde , in 1935. The original intention was to construct 20 River Class submarines for the Royal Navy, but a change of policy in 1933 prevented this.
Built at a cost of over £500 000 each, the large and comfortable River Class were partial double-hull boats with a pressure hull of 'keyhole' section.
In an attempt to keep down weight so as to obtain the required speed, the design diving depth was reduced from the 500 feet of the Odin Class to 300 feet, with the result that the pressure hull plating was reduced to 25 lb/in2 as opposed to 35 LB/in2 in Odin
To propel the River Class at the unusually high surface speed of 22.5 knots (a record at the time), and at the expense of the stern torpedo tubes, two vertical four stroke blast injection ten cylinder diesels, developing a total power of 8000 bhp at 400 rev/mm, were installed. Using two auxiliary generators, driven by two Ricardo sleeve-valve engines, these engines could be supercharged to give a total of 10 000 bhp.
The machinery was of Admiralty design and, when built, weighed 347 tons, 33 tons less than allowed for in the legend weights. Without this saving the River Class might have had serious stability problems. When first constructed, Thames, when surfacing, experienced heavy listing due to a water build-up in the main tanks on one side. The position of the flooding holes was modified to remedy this trouble. In addition, her large superstructure meant that Thames rolled heavily when surfacing 'beam on' in heavy seas, and it became the practice to surface head-to-sea in rough weather whenever possible.
As with the Overseas Patrol Submarines, the River Class carried oil fuel in external tanks, but whereas the Overseas boats were fitted with troublesome riveted tanks, the tanks of the River Class were of welded construction and were very satisfactory, though leaks occasionally occurred inboard, through rivets in the thick pressure hull plating.
With the abolition of the stern tubes, the torpedo armament of the class consisted of six 21-inch bow tubes (with 12 torpedoes carried). A 4.7-inch gun was originally fitted, but in keeping with submarine policy of the period was changed, after completion, to a 4-inch OF gun with 120 rounds of ammunition.
All three River Class submarines served in the Second World War and, although misemployed in the North Sea and Mediterranean, were certainly successful, but no more so than other British submarines of the period that cost half as much to build and operate.
Oddly, these submarines were never used with the surface fleet, as was intended, and perhaps the highlight of their war career was the vital cargo mission to Malta in September 1941 by Clyde, carrying no less than 1200 tons of desperately needed stores.
Thames was lost on active service off the coast of Norway on 23rd September, 1940. Although the cause is unconfirmed, it is likely that she was mined. The Severn and Clyde were taken out of service whilst on duty in the Far East - in April 1945 and October 1945 respectively.
Although the River Class design proved successful in service it was soon realised that the concept was wrong, and with its passing it became apparent that, with surface capital ships being capable of 30 knots, underwater speed was to be a principal feature of future submarine designs.
In conjunction with the Fleet Submarines, 12 Small Patrol Submarines were ordered in February 1929 (eight from Chatham, three from Cammell Laird and one from Scotts) and were the forerunners of the famous S Class submarines that served so effectively in the Second World War. They were based on the saddle-tank construction of the L Class submarines, the majority of which were built by Vickers ten years earlier.