1936 - 1958: U Class
The first three U Class submarines were ordered in 1936 to serve as unarmed targets for anti-submarine vessels. But in a change of policy (perhaps with a foreboding of war) Undine, Unity and Ursula laid down at Vickers in February 1937, were modified during construction to accommodate six bow tubes (four internal and two external) so that they could undertake short offensive missions. To allow the installation of a small deck gun, the hull forward of the conning tower was reinforced. From their first sea trials, the three U boats demonstrated excellent handling and manoeuvrability, which, combined with ease of production and low cost, made the design particularly successful.
In 1939, a realisation of the inevitability of war and that the small size of the U boats made them particularly suitable for North Sea and Mediterranean operations, prompted the Admiralty to put the class into quantity production. Twelve identical vessels were ordered, but of these only four were eventually fitted with six bow tubes.
The two external tubes, and the bulbous bow they formed, were removed from the remaining boats because the notable bow wave the bulge created when running at periscope depth made it difficult to keep the boat trimmed longitudinally.
Under the 1940 and 1941 War Programmes, a further 41 U boats were ordered, but only 34 were completed. This second group of U Class submarines did not differ substantially from the first, but an approximate increase of 5 feet in the stern gave them a more streamlined shape aft and improved the flow of water over the propellers.
In addition to their four 21-inch tubes and three 0.303-inch portable machine-guns, the U boats were fitted with a 3-inch gun forward of the conning tower. However, as this was an afterthought to the original design, no separate hatch was fitted for the gun crew or ammunition. This resulted in the conning tower becoming extremely crowded before and after gun action and, if the gun crew were employed, rapid crash-diving was impossible.
The limited offensive potential of individual U boats was compensated for by the considerable number that were commissioned in a short period of time, and these small and nimble vessels became one of the most important operational classes in the Second World War, with a record that can fairly be described as heroic.
The wartime submarine fleet relied almost entirely on the S, T and U Classes. This policy was very different to that of the First World War (when some 12 new classes were developed), and was pursued so as to cause the minimum interference with the shipbuilders' production programme.
The majority of the 49 commissioned U boats (all but two of which were built by Vickers) served with the Second Flotilla based at Malta, and achieved notable successes against warships and merchantmen. Two U boats, stationed in the Sicilian Channel, sank several major Italian merchant ships, which were transporting troops and supplies to Africa. Like other British boats, the U Class were particularly successful against submarines - in the Mediterranean alone, five Barrow-boats (Upholder, Ultimatum, Unbeaten, Unruly and United) sank a total of eight: six Italian and two German.
During the war, 19 boats of the class were lost on active service - 13 in the Mediterranean and six in the Atlantic and North Sea. Another submarine Untamed, sank in May 1943, but was salvaged two months later and returned to service as HMS Vitality. From 1941, numerous boats were ceded to Poland, USSR, Holland, Norway and Free France, and of these several were lost in action.
One U Class submarine that is famous for the part it played during the Second World War is the Vickers-built Upholder, which probably had the finest fighting record of any Allied submarine of the period.
After the war, many of the surviving U Class submarines were put into reserve or lent or sold to other countries. Some boats were later returned by foreign navies to be scrapped and the last of the Royal Navy U boats were broken up in 1950.