Costing an estimated £125 000, the G Class were twin-shafted vessels, with two eight-cylinder diesels that together generated 1600 bhp, giving a surface speed of 14 knots. Two single armature motors, each of 420 bhp, gave a submerged speed of 9 knots. The class carried 200 cells in two battery tanks, which gave a submerged endurance of 95 miles at 3 knots.
Early war experience gained by other classes led to the proposed G Class armament being changed to two 18-inch bow tubes, two 18-inch beam tubes and one 21-inch stern tube. This signalled the beginning of the 21-inch torpedo in Royal Navy submarines, although the experimental submarine Swordfish - ordered from Scotts a year earlier, but launched after G1 - was also fitted with 21-inch tubes. The class also carried one 3-inch Quick Fire High Angle (QF HA) gun which was fitted just forward of the bridge and a portable 2-pounder which could be fixed to a pedestal at the after end of the bridge.
Living conditions on board were considered by crew members to be good - because the G boats boasted such luxuries as an electric oven!
Although the designed diving depth of the G Class was given as 200 feet, the operational depth was probably 100 feet. However, it was noted that 'in an exceptional circumstance, one G boat dived to 170 feet when chased by mistake by British destroyers'.
During the First World War G7, G8 and G11 were lost on active service through unknown causes and in September 1917 G9 was sunk in error by HMS Petard off the Norwegian coast. Of those that survived, four were taken out of service at the end of the war and the remaining six were withdrawn from service in January 1921.
The Nautilus 1913-1919
Nautilus was a bold experiment - with an increase in surface displacement and a step change from the saddle tank type of construction to a double hull. She was a twin shaft vessel with two Vickers diesel engines, each of 1850hp, two main motors of 500hp and 352 Exide cells in two battery tanks.
The Nautilus, renamed N1 in June 1917, was designed by Vickers to have good sea-keeping qualities for extended operations in all weather conditions. Regarded by submarine officers as an exceedingly interesting experiment, Nautilus was laid down in March 1913 and, with an overall length of nearly 260 feet, was twice the size of any existing submarine.
The estimated cost of building Nautilus is given as £203 850 but, because of the extended building time, the changed that occurred, the increase in displacement and additions such as hydroplane guards, this figure was undoubtedly exceeded.
Although the designed surface speed is given as 17 knots, it is doubtful whether any reliable in-service figures for speed and endurance were obtained since she did not complete until October 1917 and had little, if any, service as an operational submarine. Her designed diving depth is given as 200 feet and compared with that achieved by previous classes this would seem to be reasonable.
Her armament consisted of two 18-inch bow torpedo tubes, four 18-inch beam tubes and two 18-inch stern tubes (with 16 torpedoes carried). A 3-inch High-Angle (HA) gun was fitted on the superstructure just forward of the bridge and this was raised and lowered on a vertical ram. It is said that Nautilus was a failure. This may be true in that she had little real service experience, being used mainly as a Depot Ship for instructional purposes. However, Nautilus was significant because the step from small to large size submarines with greatly increased engine power had been taken and this provided considerable experience and confidence for building later classes.
