The third is the “Sous-Marin autonome à grand rayon d’action,” and is represented by the _Narval_ type of vessel. They can be used both as ordinary torpedo-boats or submarines. We have in our classifications adopted the terms “submarine” and “submersible.” In designing the _Narval_ M. Laubeuf aimed at producing a disappearing vessel, which should correspond with the sea-going torpedo-boat in the same way as the _Morse_ is partly designed to replace the torpedo-boat for coast defence. The _Narval_ possesses various radii of action. 1. On the surface and propelled by its steam engine— 252 miles at a speed of 12 knots for 21 hours 624 miles at a speed of 8 knots for 78 hours 2. Submerged and propelled by electricity— 25 miles at a speed of 8 knots 72 miles at a speed of 5 knots The hull of the _Narval_ is peculiar, being double. The interior hull is of thick steel sheets: it has a circular section, and ends in a point at its two extremities. The outer hull which envelopes it is of thin sheets; its form is that of the _Gustave Zédé_. The external hull is pierced with holes above and below, and at the two ends, and the sea water circulates freely between the two hulls, which allows the ship to receive a hail of small projectiles without suffering from them, the rents in its outer hull making no change in its situation. The boat is brought to the awash condition by taking in water ballast and is steered below the surface by four horizontal float-board rudders, arranged systematically on each side of the ship, two towards the bows and two towards the stern. These “dip-rudders” are manipulated by means of a hand-wheel placed at the centre of the ship. The _Narval_ is not cylindrical in shape like the _Morse_, and her upper works are flat and form a deck. The principal dimensions of the _Narval_ are as follows:— Length 111 ft. 6 in. Extreme beam 12 ft. 4 in. Displacement { 106 tons when light. { 200 tons completely submerged. The motive power on the surface is supplied by a triple-expansion steam engine of 250 horse-power constructed by Messrs. Brule and Co. It has a water-tube boiler of the Seigle type having five injectors for stoking with heavy petroleum. In the original project the boat was to have been propelled on the surface by steam machinery of 300 i.h.p., the stoking being with compressed coal, but it was afterwards decided to supply liquid fuel. Submerged the motive power is an electro-motor, the current being supplied by 158 accumulators of the Fulmen type, which can be recharged by the motor, worked as a dynamo by the petroleum motor.