These submarines designed for Coastal duties was the first major production (38 submarines in all) for the Royal Navy, These submarines were considered for harbour defence and a alternative to minefields. This was the idea of Admiral Fisher. This design was slightly larger than the B class. and a major difference was it had two periscopes one for a continues look out and one for the commanding officer.
Displacement: 288 tons surfaced and 318 tons submerged. Speed: 13 knots on the surface and 7.5 knots submerged. Range: 1000 nautical miles on the surface at 8.75 knots. Powered by a Vickers Petrol engine giving 600hp on surface and 300 Hp submerged. Compliment: 16 Armament: two 18-inch Torpedo Tubes and carried four torpedoes.
Both pics taken alongside a "depot ship" in Harwich 1910.