HMS D7 was one of eight D-class submarines built for the Royal Navy during the first decade of the 20th century.

Description
The D-class submarines were designed as improved and enlarged versions of the preceding C class, with diesel engines replacing the dangerous petrol engines used earlier. D3 and subsequent boats were slightly larger than the earlier boats. They had a length of  overall, a beam of  and a mean draught of . They displaced  on the surface and  submerged. The D-class submarines had a crew of 25 officers and ratings and were the first to adopt saddle tanks.

For surface running, the boats were powered by two  diesels, each driving one propeller shaft. When submerged each propeller was driven by a  electric motor. They could reach  on the surface and  underwater. On the surface, the D class had a range of  at .

The boats were armed with three 18-inch (45 cm) torpedo tubes, two in the bow and one in the stern. They carried one reload for each tube, a total of six torpedoes.

Construction and career
D7 was laid down on 14 February 1910 by Chatham Dockyard, launched 14 January 1911 and was commissioned on 14 December 1911. D7 torpedoed the German submarine  on the surface with a single shot from  off the North coast of Ireland on 12 September 1917. The torpedo was launched from the stern torpedo tube. Then on 10 February 1918, D7 was mistakenly depth charged by the destroyer  but she survived. D7 collided with a U-boat in May 1918. Her periscopes were damaged but she escaped otherwise unscathed. D7 was sold on 19 December 1921 to H. Pounds.

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British D-class submarines
1911 ships
Royal Navy ship names