In this case invisibility is the element of success. Admiral Sir Cyprian Bridge, G.C.B., in a letter to the Author once said: “When submerged the concealment of the submarine is practically perfect. If she has not been sighted up to the moment of diving, she will almost certainly reach, unobserved, the point at which she can make her attack.” And this opinion—shared for many years by all experts—has been amply proved in the present war.
A submarine must, however, blend with the surrounding sea in its ever-varying colours, lights and shades, in order that she may be as invisible as possible when cruising on the surface. The French Naval Authorities experimented off Toulon with a luminous paint of a sea-green colour; but this, although causing the hull to be almost totally invisible in certain weather, was found to be useless, as, on a bright day with a blue sky, the green showed up clear against the bluish tint of the surrounding sea. After many months of experimenting, a pale, sea-green, non-luminous paint was chosen as the best colour for French submarines. The British Admiralty also carried out a few experiments in this direction, and came to the conclusion that a dull grey was the most invisible shade. The German authorities decided in favour of a grey-brown.
When travelling submerged, with only the thin periscopic tube above the surface, it is almost impossible to detect the approach of a submarine before she gets within torpedo range; and when cruising on the surface she is equally as invisible at a distance of a few miles. These qualities enable the submarine in nearly all cases where her speed permits, to effect a surprise attack on a hostile battleship or cruiser when not closely screened by fast destroyers, whose duty it is to be ever on the watch for submarines.
As to the tactics which would be employed by a submarine (or flotilla) in attacking a hostile warship (or fleet), it is impossible to say, for, like the impromptu attacks of all “mosquito craft,” the exact method, or manœuvre, is arranged to suit the circumstances, and it is very seldom that two such attacks are carried out alike. Generally speaking, however, a hostile warship could be easily sighted, on a fairly clear day, from the flying-bridge of a submarine at a distance of 10 miles; but it would be practically impossible to detect the submarine from the deck of a warship at that distance. On sighting her object of attack the submarine would sink to the “awash” condition, and proceed for from 2 ½ to 5 miles, as might be deemed expedient. She would then submerge and steer by her periscopes, each of which has a field of vision of 60 degrees. He would be a very keen look-out who would be able to detect the few square inches of periscopic tube at a distance of three miles. As this distance lessened, it might be advisable, if the sea was very calm and if the object of attack was stationary, for the submarine to slacken speed, so as to prevent any spray being thrown off by the periscopic tube. Assuming, however, that the optical tube was seen by the enemy, it would be extremely difficult to hit it with gun-fire at a distance of one or two miles, or to damage the boat itself, which would probably be immersed to a depth of 12 or 15 feet. At a distance of about 2,000 yards, or just over one mile, the submarine would discharge her first torpedo, following it up with another at closer range from the second bow tube. A rapid dive would then probably be necessary in order to avoid the hail of shot which would plough up the waters around her. If the first two torpedoes missed their mark the submarine might either dive completely under the object of attack and then fire her stern tubes at close range, or else manœuvre below the surface for an attack from some other point.
One of the effects produced on fleets or individual warships in war time by the ever present possibility of submarine attack is, however, that they never remain at anchor or even stationary in an exposed position, and seldom—if wise—proceed without destroyers as advance and flank guards. These precautions double the difficulties of a successful submarine attack.
CHAPTER IX
ANTI-SUBMARINE TACTICS
In all warfare, new weapons of attack are, sooner or later, met by new methods of defence. The submarine and the aeroplane are at present the only weapons against which there is no true means of defence, and yet one is being used as an antidote for the other without, however, any very striking success so far. The seaplane may be able to distinguish the dark patch in the sea caused by the hull of the submarine in clear water, but she cannot destroy it, neither can she signal the exact locality to an accompanying destroyer flotilla, owing to the speed with which seaplane and submarine pass over and under each other; furthermore, in rough weather or in shallow muddy water no sign of the submarine when submerged is visible from above. The great value of the seaplane as an antidote for submarines lies, however, first in the fact that the water of the open sea is usually clear, and the submarine shadow is visible from above, and, secondly, in the great speed of these aircraft which enables them to quickly cover miles of sea in their search for hostile submarines and to report their presence in a given locality by wireless to all ships operating within range.
When the enormous superficial area of a zone of war, such as the North Sea and English Channel, is duly considered, however, the difficulty in quickly and reliably locating from the air the few scattered “submarine shadows” will be easily realized. To make this method of locating submarines even fairly reliable an enormous fleet of seaplanes would be required. Again seaplanes do not, in themselves, constitute a means of defence against submarine attack, they merely increase the likelihood of detection, but, in actual warfare, it has now been proved that for every submarine detected by seaplanes two others pass quite unobserved.
Many means of attack on submarines have been proposed; and no doubt some of these, in certain cases, would prove effective; but none can be relied upon. Therefore, one of the points in favour of the submarine still remains without its antidote. This is the moral effect; for if there is no absolutely reliable means of defence, there can be no feeling of security for surface warships or merchant vessels when anywhere within the danger zone of the submarine.
Let us now examine briefly what practical methods of defence a modern warship has against submarine attacks. Great speed is undoubtedly a surface ship’s most reliable defence; and when combined with a frequent change of course, would greatly reduce the chances of a successful under-water attack. Should hostile submarines be on the line of advance they would not know whether to wait and chance the enemy approaching within torpedo range or whether to run to starboard or port. This is, if the surface warship was steaming in an erratic course—not a zigzag course, for then it might be possible to estimate, within torpedo range, the position of the ship at a given point if the “tacks” were regular.