Submarine Warfare of To-Day

zone of operations.

In the first year of the war the U-C boats discharged their cargoes of mines as soon as they could reach their respective areas of operation. The mines were usually laid close together in one field, frequently situated off some prominent headland, or at a point where trade routes converged. Then the enemy learned to respect the British minesweeping and patrol organisation, and endeavoured to lay their “sea-gulls’ eggs” in waters which had been recently swept, or where sweeping forces appeared to be weak in numbers.

When this failed they played their last card, scattering the mines in twos and threes over wide areas of sea. To meet this new mode of attack large numbers of shallow-draught M.L.’s were employed to scout for the mines at low water.

It was about this time that the great Allied mine barriers across the entrances and exits to and from the North Sea were completed and the losses among the U and U-C boats became heavy. A rapid abatement in the submarine offensive soon became apparent, and utter failure was only a matter of time.

CHAPTER XII The Mysteries of Minesweeping Explained

The task which confronted the naval minesweeping organisations in the years succeeding 4th August 1914 was an appalling one. Any square yard of sea around the 1500 miles of coast-line of the British Isles might be mined at any moment of any day or night. There were, in addition, the widely scattered fields laid by surface raiders like the Wolfe and the Moewe, which, as described in a previous chapter, extended their operations to the uttermost ends of the earth. A wonderfully efficient patrol of the danger zones had its effect in reducing the number of submarine mine-layers available to the enemy and in rendering both difficult and hazardous the successful execution of their work, but neither a predominant and subsequently victorious fleet, nor an equally skilful and alert patrol, could guarantee the immunity of any considerable area of sea from mines.

The Germans laid many thousands of these deadly and invisible weapons in the 140,000 square miles of sea around the British Isles alone in the face of over 2000 warships. To search for these patches of death in the wastes of water may well be likened to exploring for the proverbial “needle in a haystack.” Yet the sweepers, whose sole duty it was to fill this breach in the gigantic system of Allied naval defence, explored daily and almost hourly, for over four years, the vast ocean depths, discovering and destroying some 7000 German mines, with a loss of 200 vessels of their number. The result of this silent victory over one of the greatest perils that ever threatened the Sea Empire was that some 5000 food, munition and troop ships were able to enter and leave the ports of the United Kingdom weekly with a remarkably small percentage of loss from a peril which might easily have proved disastrous to the entire Allied cause.

This, then, in broad outline, was the task which confronted this section of the naval service, and its successful accomplishment forged a big link in the steel chain encompassing the glorious victory.

Before passing on to describe the ships and the appliances used it is first necessary to give a more detailed account of the operations generally included under the heading of minesweeping. As it was impossible to tell exactly where mines would be laid from day to day, an immense area of sea had to be covered by what was known as exploratory sweeping. This consisted of many units of ships emerging from the different anti-submarine bases almost every day throughout the year and proceeding to allotted areas of water, where they commenced sweeping north, south, east or west, in an endeavour to discover if the areas in question were safe for mercantile traffic. If no mines were discovered that particular area would be reported safe, but if only one of these weapons was cut from its mooring by a sweep-wire the area would be closed to merchant ships until the sea around was definitely cleared of the hidden danger. This system of open and closed areas entailed an enormous amount of efficient administrative staff work apart from the actual sweeping, and its success was partly dependent upon the vigilance of the patrols employed to divert shipping from dangerous patches of sea.

When a mine-field was discovered which interfered with the free movement of a large number of ships a big concentration of sweepers from all the adjacent bases was ordered by telegraph and wireless. The area was isolated by patrols and the mines swept up. In one field no less than 300-400 mines were known to have been laid. Finally a further exploratory sweep was made, and if nothing further was discovered the area was again opened to traffic, and the sweepers turned their attention either to routine duties or to the clearance of another field.

The entrance to every important harbour was swept once or twice a day, and all convoys had sweepers ahead of them when they left or entered such confined waters. The seas adjacent to harbours and naval bases were searched at low water for mines which might be showing above the surface. Around the anchorage of the Grand Fleet in Scapa Flow a wide belt of sea was kept clear of mines so that at any moment the fleet could reach blue water without risk from these weapons. The same precautions were taken off the Firth of Forth for the benefit of the battle cruisers, and outside Harwich for Admiral Tyrwhitt’s light forces.

^{Thornycroft & Co., Ltd.}

^{Model of a Coastal Motor Boat (55 ft.) with Torpedo and four Depth Charges}

A passage known as the “war channel”—about which more will be said later—extending from the Downs to Newcastle, was swept daily by relays of sweepers operating from the anti-submarine bases along this 320 miles of coast-line. This buoyed and guarded channel formed a line of supply for the great fleets in the north.

Each big fighting formation was provided with a special flotilla of fast fleet sweepers, which were capable of clearing the seas ahead of the battleships and cruisers moving at 20 knots. This was a separate organisation to what may be described as the routine sweeping of the trade routes. These vessels were always within call of the fleets they served.

It has been estimated that over 1000 square miles of sea were swept daily by the anti-mine fleets of the British navy during the four years of war. This may not sound a very stupendous figure compared with the area of the danger zone, but in practice it necessitated terribly hard work from dawn to dusk by several thousand ships and many thousands of men in summer heat and winter snow.

There was in addition to all this the clearing of British mine-fields no longer required in the positions in which they had been originally laid. This was not entirely an after-the-war problem, for although the great mine barriers were left until peace was assured, there were fields of minor importance which had to be cleared to meet new situations as the years of war passed swiftly by. A notable instance of this was the destruction of a big field of some 400 mines off the Moray Firth.

The foregoing refers only to the minesweeping in the principal danger zones in British waters, no account being taken of the work carried out by Allied vessels in the Mediterranean, off the coasts of France, Italy, Greece, Gallipoli, and in such distant seas as those washing the shores of New Zealand, Australia, Hong-Kong, Japan, Singapore, Bombay, Aden, the Cape of Good Hope, the United States, Eastern Canada, West Africa and Arctic Russia, in all of which mines were laid by surface raiders like the Wolfe, and afterwards located and cleared by Allied warships.

From the foregoing some idea of the gigantic nature of the task will be obtained, and we can pass on to a more detailed account of the actual work. Minesweeping may be divided into eight well-defined sections, as follows:—

(1) Fleet Sweeping.—Keeping clear the sea routes of the battle fleet.

(2) Exploratory Sweeping.—Searching the sea for isolated groups or fields.

(3) Routine Sweeping.—The daily or weekly sweeping of areas, channels and coastal trade routes, largely used by shipping.

(4) Clearing Large Mine-fields.—Big concentrations of ships to rapidly clear important routes temporarily blocked by large mine-fields.

(5) Special Shallow-Water Sweeping.—Such as that carried out off the Belgian coast by specially constructed shallow-draught ships, frequently with single-ship sweeps.

(6) Convoy Sweeping.—Precautionary sweeping in front of incoming and outgoing convoys. This was regularly done even if the fair-way was covered by routine sweeping.