These charts are drawn and calculations made assuming the following points:—
(1) The weather—fine and bright. (2) Not taking into consideration strong tides, currents, etc. (3) The enemy on the alert. (4) Submarine waits at point “D” in an awash condition. (5) Owing to 1, 2, and 3 above, the submarine travels from point “D” in all courses in a submerged condition.
The most favourable position for a submarine flotilla is to manœuvre close up to a fleet at anchor, or to get within 1,000 yards of a fleet—steaming across its course; but both of these ideal positions for attack are extremely difficult to obtain, and consequently in all the less favourable positions speed is the deciding factor. Strategems will undoubtedly play an important part in submarine warfare. An example of this has already been afforded when the German submarines resorted to the dishonest trick of laying in wait behind a trawler engaged in laying mines, over which the flag of a neutral state had been hoisted as a blind. This resulted in the loss of three British cruisers with over 1,000 lives. It would, however, be quite in accord with the rules of civilised warfare for a submarine to shelter behind a “decoy”; to attack simultaneously with a seaplane; or to approach an enemy behind one of its own merchant ships.
The Porpoise Dive.
The manœuvre known as the “Porpoise Dive” is merely the sudden rising of a submarine in order to enable her commander to get a better view of the surface than that afforded by the periscope. The submarine on approaching the object of attack rises quickly to the surface by the action of her horizontal rudders, then dives again, only remaining above water for a few seconds to enable her commander to get a glimpse of the enemy, and to take bearings. The submarine can then get within torpedo-range, with simply the tiny periscope projecting from the surface. This manœuvre is now seldom necessary, owing to the long and wide range of vision of the two or three periscopes fitted in modern submarines.
Difficulty of the Fixed Torpedo Tube.
With the exception of one or two vessels, which it would be unwise to specify, all the submarines engaged in the present war have what are called fixed submerged tubes. This means that the tubes from which the torpedoes are discharged are fitted inside the submarine on a line with the centre of the boat, and cannot be moved or aimed in any way apart from the boat itself. It therefore becomes necessary for the submarine to be aligned by the steering rudders on the object of attack before the torpedoes can be discharged. In simpler vein, torpedoes can only be fired by a submarine straight ahead or straight astern. Hence a submarine, with a hostile warship coming up on its beam, is compelled to turn and face its opponent (or turn its stern towards her) before delivering an attack.
Submarine Flotilla v. Surface Fleet.
It is absolutely necessary for submarines acting in company to have each its allotted task; and for a wide space of water to be left between each boat; as it is impossible, at present, for one submarine to know the exact position of another when both vessels are submerged. Therefore, if each boat was not previously instructed how to act, there would not only be the likelihood of the greater portion of an attacking flotilla firing their torpedoes at one or two vessels of the hostile fleet and allowing the remainder either to escape or to keep up a heavy and dangerous fire unmolested, but also of collision and of torpedoeing each other by accident. There is no means of inter-communication between submarines when submerged, and a battle between submarines is almost impossible.