The results of experience gained with D1, the prototype diesel-driven submarine, were incorporated in the design of the famous E Class submarines, which did such outstanding work during the First World War.
The boats were considerably larger than the D Class, to accommodate the introduction of broadside torpedo tubes, a major change in the design. Six of the later E boats were fitted as minelayers. This meant that the broadside torpedo tubes were omitted and 20 mines were carried in vertical tubes in the saddle tanks. The mines were released by a mechanism operated from inboard.
The E Class were the first British boats to be fitted with internal watertight bulkheads. These internal bulkheads strengthened the pressure hull and, as events during the war proved, the E Class were eventually designated as being capable of diving to a depth of 200 feet.
Fifty-six E Class were built between February 1911 and August 1917. Of the first twenty-six, 20 were built and completed at Barrow between January 1913 and January 1916, including two built at Beardmore's at Dalmuir and fitted out by Vickers, and six were built at Chatham. The remaining 30 were divided between twelve other shipyards who were entering the field of submarine construction for the first time, including Armstrongs at Newcastle, Cammell Lairds at Birkenhead and Scotts on the Clyde.
