British G-class submarine

The G class were a series of diesel electric submarines of the Royal Navy in World War I

They were launched between 1914 and 1917, and intended for operations in the North Sea and German Bight against German U boats.

The G class submarines were designed by the Admiralty in response to a rumour that the Germans were building double hulled submarines for overseas duties. The submarines had a partial double hull, a length of 187 feet (57 m) overall, a beam of 22 feet (7 m) and a mean draft of 13 feet (4 m). They displaced on the surface and submerged. However, the design offered little improvement in practice, the ships being notoriously slow to dive. Most of the class had their bows raised during the war to increase buoyancy and improve seakeeping. For surface running, the boats were nearly all powered by two Vickers two stroke eight cylinder diesel engines, each driving one propeller shaft. These engines were the first in the world to use Common Rail injection, using four plunger pumps to deliver a pressure up to every 90° of rotation to keep the fuel pressure adequately constant in the 'rail' (pipe) serving all eight cylinders. G14 was initially powered by FIAT diesels, but these proved unsuccessful, and were replaced by the standard Vickers engines. It was originally intended to fit more efficient four stroke MAN and Sulzer diesels to some of the class, but the outbreak of hostilities rendered such plans impossible. When submerged each propeller was driven by a electric motor. They could reach on the surface and underwater. On the surface, the G class had a range of at full speed.