1913 - 1919: Nautilus Class
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 changes 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.