Officers and men, expecting momentarily to find themselves blown into the air, stood stock-still. Then, as nothing so disastrous occurred, Schwalbe gave orders for easy astern.
The barrels, connected by a span of grass rope, had been thrown overboard from the pursued vessel, in the hope that the submarine would foul her propellers in the tangle of line. Once a blade picked up that trailing rope, the latter would coil round the boss as tightly as a band of flexible steel.
The plan all but succeeded; only the metal guards protecting the propellers saved them from being hopelessly jammed. Yet the attempt was attended with good results as far as the British ship was concerned, for by the time U75 had lost way and had cautiously backed away from the obstruction, the swift cargo-vessel had gained a distance that put her beyond all chance of being overhauled.
Infuriated by his failure, Kapitan Schwalbe went aft and descended into his cabin. He was hardly conscious of the presence of his two involuntary guests as he passed. He was thinking of the fate that had consigned him to a perilous and uncongenial task. Without doubt the vessel he had been pursuing was equipped with wireless, and by this time a number of those dreaded hornets would be tearing towards the spot. To add to his discomfiture it was reported to him that the reserve of fuel on board had seriously dwindled. In order to remain effective it was necessary that U75 should replenish her tanks before another forty-eight hours had passed.
According to his customary tactics, Schwalbe ordered the submarine to dive to sixty feet. At that depth she would be safe from any possibility of being rammed. Provided she could avoid the under-water obstructions with which the British naval authorities had sown the bed of the sea at almost every point likely to be frequented by lurking hostile submarines, she was in no actual danger.
Gaining his diminutive cabin, Schwalbe by sheer force of habit consulted the aneroid. The mercury was falling rapidly. Since he last looked, barely two hours previously, it had dropped 764 to 734 millimetres, or an inch and two-tenths. That meant that the anti-cyclone was rapidly breaking up, and that a severe gale was approaching with considerable swiftness.
U75 must submerge and seek shelter. It was impossible for her to keep at a uniform depth unless she maintained steerage-way; that meant a great demand upon her storage batteries. She could not remain on the bottom of the sea in a heavy gale, owing to the constant "pumping" or up-and-down movements caused by the varying pressure of passing waves, unless she sought a sheltered roadstead—and sheltered roadsteads were generally mined, or guarded by some ingenious device that had already accounted for several of U75's consorts.
Producing a chart of the Bristol Channel, Schwalbe unfolded and spread it upon a table. Then, in conjunction with a translation of the latest British Admiralty guide to the west coast of England, he proceeded to select what he hoped would be a snug shelter during the coming storm.
"Herr Rix!" he shouted. "I'll make for this anchorage. There's every indication of a strong blow from the nor'-east."
"This" was Helwick Channel, a deep, almost blind passage between the Glamorgan coast and an outlying submerged reef known as the East and West Helwick. In fine weather it was a short cut for traders plying between Llanelly and Swansea. In bad weather it was a place to be avoided, as far as sailing vessels were concerned. Sheltered by the bold outlines of Worm's Head, it ought to prove an ideal lurking-place until the gale had blown itself out, for there was little danger of the place being used as an anchorage, since vessels preferred to give the rock-bound coast a wide berth. On this account, it was also highly probable that the Helwick channel had not been safe-guarded by the British naval authorities.