F Class: Coastal Submarines
These boats were built with a double hull in an attempt to improve on the saddle tank design. Apart from an additional displacement of 50 tons and a stern torpedo tube, they were very similar to the V Class submarines
Only three of the class were built, the first F1 being built at Chatham.
All three of the class survived the war and ended their service as training boats at Campbeltown. F1 and F3 were scrapped in 1920, F2 was sold in 1922.