Inventions of the Great War

by A. Russell Bond

The mine itself, or the "devil's egg" as it is called, is usually a big buoyant sphere of metal filled with TNT or some other powerful explosive; and projecting from it are a number of very fragile prongs which if broken or even cracked will set off the mine. There is a safety-lever or pin that makes the mine harmless when it is being handled, and this must be withdrawn just before the mine is to be launched. In some mines the prongs are little plungers that are withdrawn into the mine-shell and held by a cement which softens after the mine is submerged and lets the plungers spring out. When the plungers are broken, water enters and, coming in contact with certain chemicals, produces enough heat to set off a cartridge which fires the mine.

PICKING INFERNAL MACHINES OUT OF THE SEA

The enemy mine-fields were often located by seaplanes and then mine-sweepers had to undertake the extremely hazardous task of raising the mines or destroying them. If they were of the offensive type, it was much better to destroy them. But occasionally, when conditions permitted, mine-sweepers undertook to raise the mines and reclaim them for future use against the enemy. The work of seizing a mine and making it fast to the hoisting-cable of the mine-sweeper was usually done from a small rowboat. Raising the first mine was always the most perilous undertaking, because no one knew just what type of mine it was and how to handle it with safety, or whether there was any way in which it could be made harmless. There were some mines, for instance, that contained within them a small vial partly filled with sulphuric acid. The mine carried no prongs, but if it were tilted more than twenty degrees the acid would spill out and blow up the mine. Such a mine would be exceedingly difficult if not impossible to handle from a boat that was rocked about by the waves.

After the first mine of the field was raised and its safety-mechanism studied, the task of raising the rest was not so dangerous. A water telescope was used to locate the mine and to aid in hooking the hoisting-cable into the shackle on the mine. The hook was screwed to the end of a pole and after the mine was hooked, the pole was unscrewed and the cable hauled in, bringing up the "devil's egg" bristling with death. Care had to be taken to keep the bobbing boat from touching the delicate prongs until the safety-device could be set.

However, this painstaking and careful method of raising mines was not often employed. Shallow-draft mine-sweepers would run over the mine-field, dragging a cable between them. The cable would be kept down by means of hydrovanes or "water kites" deep enough to foul the anchor cables of the mines. The "water kites" were V-shaped structures that were connected to the cable in such a way that they would nose down as they were dragged through the water and carry the cable under. The action is just the reverse of a kite, which is set to nose up into the wind and carry the kite up when it is dragged through the air. By means of the cable the anchor chain of the mine was caught and then the mine with its anchor was dragged up. If the mine broke loose from its anchor it could be exploded with a rifle-shot if it did not automatically explode on fouling the cable.

FLOATING MINES

When England entered the war she mined her harbors because, although she had the mastery of the sea, she had to guard against raids of enemy ships carried out in foggy and dark weather. But the mines were no protection against submarines. They would creep along the bottom under the mines. Then cable nets were stretched across the harbor channels to bar the submarines, but the U-boats were fitted with cutters which would tear through the nets, and it became necessary to use mines set at lower depths so that the submarines could not pass under them; and nets were furnished with bombs which would explode when fouled by submarines. In fact, mines were set adrift with nets stretched between them, to trap submarines. Floating mines were also used by the Germans for the destruction of surface vessels and these were usually set adrift in pairs, with a long cable connecting them, so that if a vessel ran into the cable the mines would be dragged in against its hull and blow it up.

The laws of war require that floating mines be of such a design that they will become inoperative in a few hours; otherwise they might drift about for weeks or months or years and be a constant menace to shipping. Sometimes anchored mines break away from their moorings and are carried around by ocean currents or are blown about by the winds. A year after the Russo-Japanese War a ship was blown up by striking a mine that had been torn from its anchorage and had drifted far from the field in which it was planted. No doubt there are hundreds of mines afloat in the Atlantic Ocean which for many years to come will hold out the threat of sudden destruction to ocean vessels; for the Germans knew no laws of war and had no scruples against setting adrift mines that would remain alive until they were eaten up with rust.