1916 - 1945: L Class
Delighted with the success of the E Class submarines, the Admiralty decided, in 1916, to revert to the saddle tank-type of construction, but incorporating the lessons learned from war experience. Two submarines to a new Admiralty design were ordered from Vickers in February 1916 and, being practically elongated E Class, they were called E57 and E58. However, overall improvements so distinguished the design that a new class title was adopted, the L Class, and the two boats were later renamed L1 and L2.
By December 1916, a total of 34 L Class submarines had been ordered, but of these only 27 were commissioned - L28 to L32 were broken-up after commencement and L34 and L35 were cancelled. L13 was never ordered, presumably for 'superstitious' reasons. (Memories of the K13 ?) Eighteen of the class were built at Vickers, three of which were completed in other yards.
L Class submarines can be divided into three groups: L1 to L8 with 18-inch bow and beam tubes; L14, L17 and L24 to L27, which were fitted as minelayers, with 21-inch bow tubes; and L9 to L33 (excluding the minelayers) which had 21-inch bow tubes and 18-inch beam tubes.
In addition to torpedo armament, the class carried a gun mounted on the superstructure forward of the bridge. Although the earlier boats (L1 to L8) carried a 3-inch HA gun, all the class were eventually fitted with a 4-inch gun of various descriptions - for a three-man increase in the complement: this increase meant that the L boats had a 38-man crew, but even so, they carried only one l2ft 6in collapsible lifeboat.
The L Class were the first submarines to carry some of the normal fuel stowage in external tanks. Although only about 20 tons of fuel was carried in two lightly-constructed tanks, this started the practice, which was developed in the 1920s, of carrying a large amount of fuel externally.
The main engines of the class were two 12-cylinder diesels, giving a total of 2400 bhp at 380 rev/min. Some authorities quote 2600 bhp, but this was the bench test power of the
engines. L Class submarines carried 336 cells in three battery tanks, grouped to allow working at 220 volts in series and 110 volts in parallel, producing submerged power for four main motors of the open shunt wound double-armature-type, developing a total of 1600 bhp at 300 rev/mm for 1 1/2 hours. Also, an auxiliary drive consisting of a 20-hp motor, driving the starboard shaft through a worm drive, could give a slow-running submerged speed of 1.75 knots.
A surface speed in excess of 17 knots was hoped for in the L Class and, even when carrying additional fuel in the external tanks, there is no doubt that this speed was attained. The first boat on trials, L1 , actually obtained 17.2 knots and, in 1930, 17.6 knots was given as the design surface speed for the class. Although a design-submerged speed of 11 knots was anticipated in L1, the fitting of a 5ft 6in high fixed bridge screen reduced this to 10.5 knots.
Although it has been stated that the designed diving depth of the L Class was 250 feet, the officially used maximum diving depth, in 1925, was 150 feet - based on the age of the boats, their wartime construction, etc. However, depths, in service, of more than 250 feet have been recorded and, on one occasion, L2 accidentally submerged to 300 feet and, except for minor faults withstood the pressure.
Of the L Class, only one was lost during the war - L10, in the North Sea. In August 1923, L9 foundered in Hong Kong harbour in a typhoon and was later salvaged, but was not refitted. In January 1924, L24 was accidentally rammed and sunk off Portland by the battleship HMS Resolution. At the time, prolonged efforts were made to salvage her, and a team of German divers, with a new type of diving suit, which enabled them to work in deeper waters, was brought over. Unfortunately, the strong underwater currents proved too difficult and the L24 still lies where she sank. In October 1945, L23 was the last L boat to be taken out of service 28 years after she was laid down - thus reflecting the success of he class.
The building of the L boats led to the construction of the L50 Class, which was the L Class modified to give increased armament. Although none were built at Vickers, a total of 25 L50 submarines were ordered from seven yards, but of these only seven were completed.