British submarines of WW1 were generally of three classes: C, D and E. Wikipedia The British C-class submarines were the last class of petrol engined submarines of the Royal Navy and marked the end of the development of the Holland class in the Royal Navy. Thirty-eight were constructed between 1905 and 1910 and they served through World War I. With limited endurance and only a ten percent reserve of buoyancy over their surface displacement, they were poor surface vessels, but their spindle shaped hull made for good underwater performance compared to their contemporaries. The D-class submarine was the Royal Navy's first class of submarines capable of operating significantly beyond coastal waters. They were also the first boats to be fitted with wireless transmitters. All ten were laid down between 1907 and 1910. D-class boats were fitted with twin screws for greater manoeuvrability and were fitted with saddle tanks. The D class were the first submarines to be equipped with deck guns forward of the conning tower beginning with D6. Also, reserve buoyancy was increased to 20.6%. Armament also included three 18-inch (460 mm) torpedo tubes (2 vertically in the bow and 1 in the stern). The D class was also the first class of British submarines to have standard radio fitted. The aerial was attached to the mast of the conning tower that was lowered before diving. With their enlarged bridge structure the boat profile was recognisably that of the modern submarine. The D-class submarines were considered to be so innovative that the prototype, D1, was built in utmost secrecy in a securely guarded building shed. She was launched at Barrow with equal secrecy, with only departmental heads and a few officers from the cruiser HMS Mercury, that was currently in dock being present. Once moved to the fitting out berth, she was once again screened from view. The D class were based at Harwich, Immingham, Blyth and Dover. Their wartime role was to sink German warships. In the latter stages of World War I the D class were used for training crews based at Portsmouth. During World War I the boats patrolled the North Sea and the Heligoland Bight, and protected cross channel troopships. During the war, four boats (D2, D3, D5, and D6) were lost, and the remainder (D4, D7, and D8) were paid off in July 1919. The British E class submarines started out as improved versions of the British D class submarine. All of the first group and some of the second group were completed before the outbreak of World War I. The group 1 boats of the E class cost £101,900 per hull but the price eventually increased when the second group entered service to £105,700 per hull. As submarine technology improved, the E class went through several modifications to install the new improvements which were all installed by the time the final group was under construction. The class served in the North Sea and the Baltic and Turkish operations while some served with Russian ships in Russian coastal waters before being scuttled to avoid capture by the communists who were gradually taking control of Russia. The E class served with the Royal Navy throughout World War I as the backbone of the submarine fleet and were eventually replaced by the British L class submarine. All the E class submarines were withdrawn from service by 1922.