Barely had the prisoners regained their place of confinement than the bulkhead door was shut, a slight yet distinctly perceptible list announcing that the submarine was diving. The fore-peak was now uncomfortably crowded, for the "watch on deck," unable to remain any longer on deck, had come below at the order to trim ship for diving. One and all looked drawn and anxious. Unlike their brethren in the non-mine-laying submarines they had practically nothing to do. The excitement of being able to launch a torpedo at a British ship, be she naval vessel or merchantman, was denied them. They were, in fact, nothing more than passive individuals cooped up in the shell of a submerged craft, unable to see what was going on without, and helpless to save themselves in the event of the submarine being rammed.
For quite a minute the obliquely downward plunge was maintained, the vessel the while turning sharply to starboard. Then, pitching slightly to the violent displacement of a volume of water, she resumed her normal trim at a depth of ten fathoms beneath the surface.
The action of porting helm had undoubtedly saved the mine-laying submarine. An alert British patrol boat had sighted her from afar, and at a rate resembling that of a train had charged down upon the spot where UC49 had disappeared, while trailing astern at the end of an insulated cable was an explosive grapnel of sufficient power to shatter the submarine's hull like an egg-shell.
The skipper of the patrol boat had made due calculations to ensure, as he thought, the destruction of his prey, but he had not reckoned upon the UC49 changing course as she dived. As it was, the explosive grapnel passed within a couple of yards of the submerged vessel's beam.
Of this Fuller and his companion knew nothing. Perhaps, for their state of mind, it was as well. A man will bravely face death at the hands of his foe, but he will jib at the idea of being "snuffed out" by his own side.
Slowly the minutes passed. UC49 was still running submerged, increasing the depth to twenty fathoms and maintaining a zig-zag course in order to baffle her pursuer. The German seamen were beginning to breathe more freely. The worst part of the business—the great risk of being rammed as she dived—was over, and although under the enormous pressure jets of water were hissing through the faulty joints the men realised that they stood more than a fighting chance of evading destruction.
For perhaps five hours UC49 blindly made her way under the waves. The captives had lost all count of time. Their watches had stopped owing to their immersion when the seaplane was sunk; there was no clock in the fore compartment nor were the bells struck in the customary style on board. But at length, after a seemingly interminable interval, the order was given to empty the auxiliary water ballast tanks. Simultaneously the floor assumed a list—this time in a contrary direction.
Then, without warning, the fairly regular throb of the electric motors gave place to a discordant jar that shook the hull from end to end.
"Main shaft gone, for a dead cert," exclaimed Kirkwood. "I remember the same thing occurring on the 'Tremendous's' picket-boat Yes, they're switching off."
The mine-layer was helpless. Without means of propulsion there were only two courses open to her—to float or sink to the bottom. It was impossible to keep submerged to a certain depth simply by means of admitting a certain quantity of water ballast. Once the reserve of buoyancy was overcome she would sink to the bed of the North Sea, in all probability collapsing under the terrific pressure on her hull long before she arrived there. It is only by means of the diving rudders acting in conjunction with her diving trim that a submarine can remain submerged to a required depth; and since the kapitan-leutnant of UC49 had no desire to make the acquaintance of the floor of the ocean other than by means of an "armed" lead-line, he chose the other alternative and rose to the surface.