The rounds passed on. The sentry resumed his walk without attempting to give the salute. This Hamerton noticed particularly. As in the British Army, it was forbidden to give or acknowledge compliments after sunset. This knowledge he hoped to profit by, since it was within the bounds of possibility to impersonate a German officer and thus get safely away in one of the boats at the beach of the Unterland.
"Now!" whispered the Sub once more.
Silently the two comrades made their way to the fence. This time the lowermost wire was set up taut, and Hamerton had the greatest difficulty in holding it up sufficiently for Detroit to crawl clear of the sharp barbs. Before the sentry had set out on his return beat the fugitives had put a safe distance between them and that particular danger.
They were now within a hundred yards or so of Sathurn, the northernmost part of Heligoland, that terminates in a sheer cliff one hundred and sixty-six feet in height. Close to the point rises a detached pinnacle of rock, known as Hengst, its summit being only three feet lower than that of Sathurn.
"You stop here," whispered Hamerton. "The sentries seem as thick as flies. I'm going to crawl a few yards. One may escape detection where two will not."
With this injunction the Sub left his companion, and on all-fours made his way towards the extremity of the cliff. On his left was a building that a few years previously had been used as a fog-signal house. A light was burning within, and the sharp click of a shutter told the Sub that someone was using a Morse signalling apparatus.
Profiting by the glare, Hamerton crawled closer. The door of the hut was ajar. Within were several engineers standing by in readiness to work a powerful searchlight. To the left of the hut, and protected from leeward by a mound of earth, was a long metal cylinder about eighteen inches in diameter. A stray beam of light showed Hamerton that one end of this object was carefully covered by a tarpaulin.
"What's this arrangement, I wonder?" he thought. "Looks like a sort of torpedo tube. I'll——"
His hands clutched at empty air, he lurched forward, up went his heels, and the next instant he felt himself falling.
Like a flash the thought went through his brain: "I'm done for this time—I've toppled over the cliff." Yet not a sound escaped his lips, even when completely taken aback by the sudden plunge.