Submarine Warfare of To-Day

by Charles William Domville-Fife

  The introduction of what became known as “delayed action mines”—weapons held down on the sea-bed, after being launched, for varying periods of time, so that sweeping operations might take place above them without their being discovered; then, when the time for which the delay was set had expired, they rose to within ten feet of the surface and became a great danger to shipping in places recently swept and reported clear—caused a new form of sweep to be devised and used in waters where these mines were likely to be sown.

  Fig. 27.—Diagram showing mine mooring being cut by sweep-wire. A. Mine-mooring wire. B. Hard and cutting face of sweep-wire. The dotted lines C show how the mine floats to the surface by its own buoyancy when the mooring wire holding it down has been cut.

  This type of sweep was known as a “bottom sweep,” and generally consisted of a chain fitted into the bight of a sweep-wire and dragged along the sea-bed, the idea being to overturn the delayed mine and so upset its mechanism that it would either rise immediately to the surface or else remain for ever harmless at the bottom of the sea. In many cases the heavy chain passing over the horns of the mine would bend and make them useless, so destroying the efficiency of the mine even if it did eventually rise to the correct firing depth.

  Into almost every operation carried out on or under the sea there enters the tide difficulty, and in all mining and minesweeping operations it is one of the most important factors to be considered. The effect of the tide on mine-laying has been dealt with in a previous chapter, and the same difficulties in reverse order are experienced when sweeping the sea for these invisible and dangerous weapons. It has already been shown that a vessel may sometimes pass safely over a mine at high water which would touch her sides or keel and explode if she passed over it at low water when the mine was nearer to the surface. All minesweeping vessels, therefore, need to be of comparatively shallow draught in order to reduce the risk of touching mines, but against this is the fact that shallow-draught ships, even if powerfully engined, have but little grip on the water and experience an undue loss of speed when towing a heavy sweep-wire. Such vessels can seldom operate in even moderately heavy weather owing to their rolling and pitching propensities. Therefore a vessel of medium—bordering on shallow—draught, with a fairly broad beam, is the best type. Here, again, is a difficulty. Minesweeping is a type of defensive warfare requiring a vast number of ships successfully to carry on against an enemy well provided with surface and submarine mine-layers, and not even the greatest naval power in the world could seriously contemplate maintaining a peace fleet of, say, 2000 such vessels in constant readiness. Therefore recourse has to be made, when war comes, to mercantile craft, which seldom possess all the desired qualities.

  This is what actually occurred in every maritime country at war during the years succeeding August, 1914, and in order to meet the danger attending the use of passenger ships, trawlers and drifters, often with a considerable draught, minesweeping operations were, whenever possible, confined to the three hours before and the three hours after high water. Shallow-draught M.L.’s carried out the scouting for mines at low tide. It is difficult to see what would be the fate of a nation hemmed in by mines and devoid of a mercantile fleet sufficiently numerous to provide powerful sweeping units. The trawlers and pleasure steamers were a godsend to England in those years of intensive submarine warfare. This undeniable fact incidentally provides another example—if such is now needed—of naval power resting not entirely on fleets and dockyards, but on every branch and twig of maritime activity.

  It is difficult to describe in small compass and non-technical language the various tactical formations employed in minesweeping operations. They were many and various. The Germans used their vessels in long lines, the ships being connected together by a light wire-sweep plentifully supplied with cutting devices, into which the mooring wire of the mine was expected to obligingly slip. This method suffered from the serious drawback that if any part of the sweep-wire caught on a submerged obstacle, such as a projection of rock, the whole line of ships became disorganised. There were also many other objections to this system, some of which will doubtless be apparent to the thoughtful reader.

  The formation usually adopted by British minesweepers was that shown in Fig. 28, in which it will be observed that each pair of ships is actually independent of the others, but is acting in company with them, and that the pathway swept by one pair is slightly overlapped by the following pair. In the event of an accident to one ship the next astern can immediately let go its own end of sweep-wire and go to the rescue of any survivors. It may be apropos to say here that the smaller class of minesweeper is usually blown to pieces if she touches a mine.

  Fig. 28.—Plan showing the usual formation adopted by British minesweeping vessels. A. Three pairs of sweepers. B. Sweep-wires. C. A mine entering the sweep of the second pair. D. A vessel following the sweepers for the purpose of sinking by gun-fire the mines cut up.

  The set of the tide is another important factor which has to be taken into serious consideration when plotting a sweep. This complication enters into every operation, and its salient points will be made quite clear by referring to Fig. 29.

  The actual speed at which minesweeping operations are carried out depends greatly upon the engine-power of the sweepers themselves. In the case of trawlers and drifters it is seldom possible to drag the 300-600 feet of heavy wire through the water at a greater rate than 4 to 6 knots. M.L.’s can accomplish 8 knots with a lighter wire, while big fleet sweepers with engines of several thousand horse-power can clear the seas at 18-23 knots.

  Fig. 29.—Diagram illustrating the effect of tide on minesweeping operations. A. The vessels sweeping along the coast-line B. A fast ebb-tide is coming down the estuary C. Unless an allowance was made for this tide and mark-buoys or ships were placed along the dotted course D, the sweepers would unknowingly drift seawards along course E, leaving a space F unswept and possibly dangerous to ships entering and leaving the estuary C.

  Sufficient has now been said to enable the reader to realise fully the arduous, exciting and often very hazardous nature of the work. Veteran sweepers listen for the loud hum of the wire which proclaims that a mine has been caught. Then comes an interval of a few seconds of suspense. Sometimes the mine bobs up within a few feet of the ship; at other times it is in the middle or bight of the wire, far astern, and half-way between the two sweeping vessels. When a mine is cut up a few shots from a 3-pounder, a shattering roar and the mine is destroyed. All that remains is a column of smoke reaching from sea to sky.

  It frequently happened that the mine became entangled in the sweeping gear and was unknowingly hauled on board with the sweep. When this occurred the position was fraught with extreme peril. Any roll of the ship might cause an explosion which would shatter to fragments everything and everyone within range. Safety lay in lowering the sweep gently back into the sea—an extremely difficult operation on a rough day.

  The War Channel

  This carefully guarded fair-way consisted of a 320-mile stretch of sea, extending along the east coast of England from the Downs to Newcastle, which was marked on the seaward side by a continuous line of gigantic buoys, two miles apart. It was patrolled day and night by hundreds of small warships, and swept from end to end by relays of sweepers acting in conjunction with each other from the different anti-submarine bases along the coast.

  The war channel formed a comparatively safe highway for all coastal shipping passing north or south through the danger zone, and vessels from Holland, Denmark, Norway and Sweden were able to cross the North Sea at any point under escort and proceed independently and safely along the British coast to whichever port could most conveniently accommodate them at the time of their arrival. It also relieved the terrible congestion on the railway lines between the north and south of England by enabling a coast-wise traffic to be carried on between the ports of London, Grimsby, Hull and Newcastle, as well as enabling the numerous Iceland fishing fleet to pass up and down the coast in com
parative safety on their frequent voyages to and from the fishing grounds of the far north. From the naval or strategic point of view it more or less secured a line of supply for the Grand Fleet assembled in the misty north. Colliers, oilers, ammunition and food ships were able to proceed through the comparatively narrow section of the danger zone with a minimum of risk; and, had it been required, there was available a cleared passage for any squadron from the big fighting formations to come south at high speed to checkmate a bombardment or attempted landing on anything like a grand scale.

  It may perhaps be wondered why this channel was not extended up the east coast of Scotland as far as Scapa Flow. In the first place, the North Sea widens considerably as the higher latitudes are approached, the coast of Scotland does not lend itself to a clearly defined channel and the heavy weather which prevails for so many months in the year made the maintenance of gigantic buoys and their moorings almost impossible. Secondly, there were various systems of mine defences in this area, and, although not defined by a chain of buoys, the passage north from Newcastle to the Scottish islands was, in actual fact, maintained by a vast organisation of patrols and sweepers, but over this section of sea supply ships for the Grand Fleet were nearly always under escort. The area from the Scotch to the German coast was looked upon more as a possible battle-ground for the fleets at war than as a route for merchant shipping, owing to the comparatively few big commercial harbours along the eastern shore.

  Laying the moorings of over 150 gigantic buoys in fairly deep water, exceptionally prone to sudden and violent storms, was in itself a noteworthy feat of submarine engineering. The chains and anchors had to be of great strength, and the whole work, which occupied many weeks, was carried out in waters infested with submarines and mines.

  The task of sweeping this vast stretch of sea almost continuously for four years was by no means either straightforward or without risk. The Germans, when they discovered the existence and purpose of this channel, sought to turn it to their own advantage by systematically laying mines around the moorings of the mark-buoys, where they could only be swept up with great difficulty, owing to the sweep-wires fouling the moorings of the buoys. This strategem had to be answered by the creation of “switch lines,” or small sections of false channel marked by buoys, while the real channel was only outlined on secret charts. In this way the preservation of the war channel and its use for misleading and entrapping U and U-C boats became a semi-independent campaign, in the same way as that which surrounded the great mine barrages and other activities of the anti-submarine service.

  Mine Protection Devices

  It is an axiom of war that new weapons of attack are invariably met by new methods of defence. The mine was no exception to this rule, although up to the present time the various antidotes are in all cases only partial 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 manœuvred. 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 at
tempting 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.