Submarine Warfare of To-Day

remedies. During the years of war, with the brains of a maritime nation focused on the subject, there were naturally many devices suggested and tried for protecting ships from mines. The great majority of these suggestions may be classified in two groups: (1) Those which sought to deflect the mine from the pathway of the ship; and (2) those which sought to minimise the result of the explosion. One method from each of these groups was adopted with various modifications to suit different classes of ships.

In the first group came the Paravane, which had as its basis the suspension of a submerged wire around the bow of a ship, which caught and deflected the mine-mooring wire before the horns of the mine itself could reach the sides of the ship. It also cut the mooring and enabled the mine to rise to the surface and be destroyed by gun-fire.

^{Topical Press}

^{A Paravane}

^{Hoisting in the starboard paravane of the P.V. mine-defence gear.}

In order to understand this appliance it is first necessary to know what is the action of the majority of moored mines on coming in contact with a ship. It seldom happens that a vessel strikes a mine dead on the bow or stem-post. The cushion and dislocation of water formed by a big and fast ship around its bows is usually sufficient to cause the mine to swing a few inches away from the bow and to return and strike the ship several feet back on the port or starboard side. A careful study of Fig. 30 will show how this is prevented by the deflecting wires of the paravane.

The paravanes themselves are submerged torpedo-shaped bodies which hold the wires under the surface and away from the ship’s side, deriving their ability to do this from the speed at which they are being towed, submerged, by the ship itself. A piece of string through the axle hole of a small wheel, which is then placed on the ground and pulled along, will give a good idea of the action of the paravane against the passing water.

^{Fig. 30.—Plan showing the chief characteristics of the paravane mine defence gear. A. The bow of the ship. B. The paravanes being towed submerged at an outward angle. These appliances maintain a fixed depth below the surface and hold the ends of the deflecting wires C well away from the ship’s sides. C. The submerged deflecting wires, held at one end by a short projection from the ship’s stem-post below the water-line, and at the outer end by the submerged paravanes. D. A mine and its mooring caught by the deflecting wires and held away from the ship. In such a case it would slide down the deflecting wire towards the paravane, where the mooring would be cut and the mine would float to the surface.}

It is not possible to give here the exact details of this highly ingenious device upon which so much scientific and practical attention was wisely bestowed, but sufficient has been said to enable the reader to form a clear conception of how the mine was caught and held away from the ship’s side by the deflecting wire of the paravane.

This device, in one of its many forms, was fitted not only to warships, but also to many hundreds of merchantmen, and was known to have saved thousands of tons of valuable shipping and cargo.

Among those devices which had for their object the minimising of the result of a mine explosion may be mentioned the “Blister System” so successfully employed in the construction of monitors and other big ships, the idea being to surround the inner hull with an outer casing which received the effect of the explosion of either a mine or torpedo and left the inner or real hull of the ship water-tight. Its one weak feature was that it reduced the speed of the ship and the ease with which she could be man?uvred. In future types of large and heavily armed ships this drawback will undoubtedly be largely overcome by an increase in engine-power made possible by the development of engineering science.

The “blister,” although outwardly forming a continuous structure round the entire vessel, extending well above and below the water-line, tapered off towards the bows and stern, and was subdivided into different compartments. In this way an explosion against one section did not necessarily damage any other part. The British monitors which so successfully bombarded the Belgian coast and the fortifications of the Dardanelles were fitted with blisters, and more than one of them owed their salvation to this means.

CHAPTER XIII The Mine Barrage

What undoubtedly forms the most effective counter to unrestricted submarine warfare is the explosive mine barrage, as employed against the German U-boats in the North Sea and the Straits of Dover.

The practicability of these barrage systems depends, however, very largely upon the following factors:—(1) the geographical features of the area of operations; (2) the hydrographical peculiarities of the seas in which the mines have to be laid; (3) the number of properly equipped mine-laying vessels available; (4) an adequate and highly trained personnel; and (5) the mechanical skill and manufacturing power of the nation employing the system.

There are several forms of mine barrage. One is simply an elongated mine-field laid across a narrow sea to prevent the safe passage of hostile surface craft. In this case the mines are laid in the ordinary manner and at the ordinary depth below the surface. The anti-submarine barrage, however, consists of an enormous number of mines, laid at a considerable depth below the surface and in such formation as to ensure that a submarine attempting to pass through the cordon while submerged would inevitably collide with one or more of them.

With this latter form of barrage the surface of the sea is quite clear of mines and is comparatively safe for the unrestricted movement of a numerous patrol flotilla, which forms part of the system, the under-seas alone being made dangerous by the mines.

It will be apparent that if a hostile submarine base is enclosed by one or more of these barrages the under- water craft entering and leaving that base have the choice of travelling submerged across the danger zone and thereby risking contact with the mines, or of performing the passage on the surface and encountering the patrolling ships. In either case, the result is more likely than not to be the destruction of the submarine.

In most cases the exact position of the barrage would be unknown to the hostile submarines, which, even if running on the surface, would dive immediately on the approach of a patrol ship. The few lucky ones succeeding in getting safely through the cordon of deep-laid mines, or passing unnoticed the patrol of surface ships on their outward journey—as might be the case in fog—would have the same peril to face on the return to their base, and probably without the aid of thick weather. This double risk would probably have to be taken by every submarine in the active flotilla at least once a month, this being approximately the period they can remain at sea without replenishing supplies of fuel, torpedoes and food.

The object of the flotillas of shallow-draught patrol vessels operating in the vicinity of the deep mine barrier is twofold. Primarily their duty is to prevent the hostile submarines from running the blockade on the surface and, secondly, to prevent enemy surface craft from emerging from the base and sweeping clear a passage through the mine-field, or of laying counter-mines, which, on being exploded, would detonate some of the blockading deep-laid mines and so destroy a section of the barrier.

From this it will be apparent that a force of hostile submarines hemmed in in this way would run a double risk of losing a number of vessels on every occasion on which a sortie was made. This is what actually occurred to the German under-water flotillas in the years 1917-1919, and, in combination with the other methods employed by the Allied navies, was mainly responsible for the failure of the great under-sea offensive.

The only bases of the German navy being situated on the North Sea littoral, it was possible for the Allies to lay a vast mine barrier, stretching from the coast of Norway to the Scottish islands, and another smaller one across the Straits of Dover; also to concentrate in the vicinity of these two submarine “trench systems” a very numerous surface patrolling force, thus enclosing the thousands of square miles of sea forming what was sometimes