Submarine Warfare of To-Day

this it will be apparent that in places where there is a strong current or tide a mine-field is only dangerous to passing ships of shallow or medium draft for a few hours (during slack water) out of the twenty-four. Between the ebb and the flow of a tide there is a short period when the water is almost still. Then the movement begins to set in from the opposite direction and gradually gains in speed until about one hour before high or low tide. This period of what is known as “slack water” varies considerably in different places and different weather conditions, but plays an important part in all minesweeping operations.

In this way many a ship has passed over a mine-field all unconscious of the fate which would have befallen her had she traversed the same area of sea an hour or so earlier or later.

Mines which break adrift, or are laid without moorings of any kind, are called floating mines. The latter are a direct violation of International Law, as they cannot be recovered when once they have been laid, and become a danger to neutral as well as to enemy shipping. The laws of civilised warfare also require even a moored mine to be fitted with some mechanical device which renders it safe when once it has broken adrift from the wire and heavy sinker which holds it in a stated position. The reason for this humanitarian rule is that neutrals can be warned not to approach a given area of sea in which there are moored mines, but if these weapons break adrift—as they frequently do in heavy weather—and float all over the oceans, they would seriously endanger the lives and property of neutral states unless something were done to render them innocuous.

The total disregard of all the laws and customs of civilised warfare by the Germans in 1914-1919 has now been so well established that it seems almost unnecessary to give yet another instance of this callousness. In the case about to be quoted, however, there is, as the reader will observe, an almost superlative cunning.

Any cursory examination of a German moored mine will show that there is a device fitted ostensibly to ensure the weapon becoming safe when it breaks adrift from its moorings and thus complying with The Hague Convention. For several months after the outbreak of war it puzzled many minesweeping officers and men why, with this device fitted, every German floating or drifting mine was dangerous. A few, relying on these weapons being safe when adrift, had endeavoured to salve one and had paid for the experiment with the lives of themselves and their comrades. This caused every mine, whether moored or adrift, to be regarded by seamen as dangerous, notwithstanding the oft-repeated assurances that German mines fulfilled all International requirements in this respect. Then a mine which had broken away from its moorings was successfully salved, in face of the great danger involved, and the truth came out.

A device was fitted to render it safe, but, with truly Hunnish ingenuity, the metal out of which an essential part of this appliance was made was quite unable to bear the strain imposed by its work, and, to make doubly sure, another part was half filed through. The result was that, instead of rendering the mine safe when torn from its moorings by rough seas, the essential parts broke and left the mine fully alive.

Any discovery such as this—only made at the great risk of salving a live mine— could be easily explained away by German diplomacy as faulty workmanship in a particular weapon, reliance being placed on the fact that not many mines could be salved in this way without heavy loss of life; but numbers were recovered in spite of the dangers and extraordinary difficulties of such operations, and the guilt was for ever established in the minds of those who sail the seas.

Little need be said here regarding the method of laying mines from surface ships like the Wolfe and Moewe. The weapons were arranged to run along the decks on railway lines and roll off the stern, or through a large port-hole, into the sea as the vessel steamed along.

With submarine mine-layers or U-C boats the method was, however, much more complicated and needs full description. Each vessel was fitted with large expulsion tubes in the stern and carried some eighteen to twenty mines. These weapons, although similar in their internal mechanism to the ordinary mine, were specially designed for expulsion from submerged tubes or chambers.

The mines were stored in the stern compartment of the submarine, between guide-rails fitted with rollers. They were in two rows and moved easily on the well-greased wheels. The loading was accomplished through water-tight hatchways in the deck above. In order to expel these mines from the interior of the submarine when travelling under the surface each weapon had to be moved into a short expulsion tube or chamber, the inner cap of which was closed when a mine was inside, and the outer or sea-cap opened. A supply of compressed air was then admitted into the back of the tube and the mine forced out into the open sea, in the same way as a torpedo is now expelled from a submerged tube.

Before another mine could be launched the sea-cap had to be closed, the water blown from the tube, the inner cap opened and a second mine placed ready in the chamber. This, however, did not end the difficulty of laying mines from submarines. The increase in the buoyancy of the boat, due to the loss of weight as each mine was discharged into the sea, had to be instantly and automatically compensated by the admission of quantities of sea- water of equal weight into special tanks, hitherto empty, situated below the mine-tubes. If this had been neglected the submarine would have come quickly to the surface, stern uppermost, owing to the lightening of the hull by the expulsion therefrom of some fifteen weapons weighing many hundreds of pounds each.

When the mine was clear of the submarine it sank to the bottom, owing to the weight of the sinker or anchor. After a short immersion, however, a special device enabled the top half, containing the charge of explosive and the contact firing horns, to part company with the heavy lower half, composed of the iron sinker and the reel of mooring wire. The explosive section then floated up towards the surface, unwinding the wire from the sinker.

Each mine being set, before discharge, to a certain prearranged depth (obtained by the captain of the U-C boat either by sounding wires or from special charts showing the depth of water in feet), the weapon could not rise quite up to the surface, being checked in its ascent, when ten feet from the top, by the mooring wire refusing to unwind farther.

This may sound a little involved, but a careful study of the accompanying diagrams will make the various movements of the mine and its sinker, after leaving the submarine, quite clear to the lay reader.

There were also other types of mines employed. Some were fitted with an automatic device which was actuated by the pressure of the water at a set depth. These weapons could be expelled from submarines without the necessity of knowing and adjusting the depth at which they were to float below the surface. A mine of this pattern rose up, after discharge from the tube, until the pressure of water on its casing was reduced to 4? lb. per square inch (the pressure which obtains at a depth of ten feet below the surface8), and there the weapon stopped, waiting patiently for its prey.

Another kind of mine was of the floating variety—tabooed by The Hague Convention—which drifted along under the surface with no moorings to hold it in one position.

Now that the reader is familiar with the mines themselves and the actual methods of laying them, we can pass on to a brief review of the German mine-laying policy during the Great War.

The submarine offensive reached its maximum intensity in 1916-1917, during which period no less than 7000 mines were destroyed by the British navy alone.9 Of this number about 2000 were drifting when discovered. There was, with one small exception, no portion of the coast of the United Kingdom which was not mined at least once during those eventful two years, the unmined area being undoubtedly left clear to facilitate a raid or invasion. About 200 minesweeping vessels were blown up or seriously damaged, but the losses among the Mercantile Marine were kept down to less than 300 ships out of the 5000 sailings which, on an average, took place weekly.

The heavy losses inflicted on the enemy’s submarine fleets in 1917 marked the turning of the tide, and from that date onwards there was a steady but sure reduction in the number of mines laid.

During the first twelve months of the intensified submarine war the Germans concentrated their mine-laying on the food routes from the United States, the sea communications of the Grand Fleet off the east coast of Scotland and the line of supply to France. Then, when they commenced to realise the impossibility of starving the sea-girt island, and the weight of the ever-increasing British armies began to tell in the land war, the submarine policy changed to conform with the general strategy of the High Command, and the troop convoy bases and routes were the objects of special attack.

The arrival in Europe of the advance guard of the United States army caused another change in the submarine strategy. From that time onwards the Atlantic routes assumed a fresh importance and became the major