The natural features of Sandinsel Island were favourable for this work, for stretching in a north-westerly direction for almost three miles were a number of rocky ledges, many of their points drying at low tide. Already the Olde Hoven Brunnen and the Krid Brunnen were converted into firm ground faced with granite or ferro-concrete walls, while the work of reclaiming the Witt Klif Brunnen was actively progressing. Although Sandinsel had already outgrown its companion isle in point of size, reclamation works were in a state of activity at Heligoland itself. Wharves extending nearly a mile from Sathurn—the southernmost limit of the original rock—formed an efficient breakwater to South Haven; and the area thus enclosed had been adapted for the purpose of berthing twenty submarines and eighty first-class torpedo boats and destroyers attached to the Heligoland command.
The submarines were the latest creations of the renowned Krupp Germania yard—large, speedy, and capable of operating within a thousand miles of their base without having to be dependent upon fresh supplies of gasoline. Submerged, they could travel a distance that would bring them within striking range of any port on the east coast of Great Britain. They were armed, in addition to the four torpedo tubes, with two fourteen-pounders on disappearing mountings, and, as Hamerton had discovered, with high-angle pneumatic guns, so as to be able, even when submerged, to attack aircraft with a great possibility of success.
Undoubtedly the new Heligoland was a strong fortress for defence. It was more: it was a base for offence, for why were ocean-going destroyers and submarines stationed there if their sole duty was to defend the comparatively short stretch of coast line that forms the German Empire's bulwark on the North Sea?
Heligoland, like the newly created fortresses of Borkum and Westerland Sylt, was a menace, directed principally against Great Britain and the British Empire.
And by a strange freak of navigation the Diomeda had dropped anchor in South Haven. Possibly had the lighthouse been showing its powerful light Hamerton might have picked up his position even in the thick, drizzling rain; but, in accordance with notices supplied to mariners by the German Admiralty, the light was extinguished whenever night operations were in progress in the vicinity of Heligoland. The leading lights on Sandinsel and the lamps at the extremities of the Moles had likewise been temporarily discontinued; yet in spite of these disadvantages, the German authorities had the mortification of knowing that a small craft, unpiloted and unseen, had crept up to the anchorage in the dead of night.
On the face of it there could be no other explanation than that the crew of the yacht were spies. The failure on their part to show a light under the bowsprit by night, or hoist their national ensign to the masthead by day, was in itself suspicious; and, left to their own resources in their temporary prison, Hamerton and Detroit agreed that the action of the German authorities was to a certain extent justifiable.
"Directly we explain matters to the commandant we'll be released," said Hamerton; "but I don't see the fun of having to give explanations to that arrogant sweep of a major."
"Nor I," added Detroit. "And I guess I'd just like to have half a dozen rounds with that yellow-haired lieutenant. I'll bet the other fellow is having a high old time rummaging our belongings."
The Sub did not reply. Again the thought of what might happen if the compromising Schwartz-Kopff torpedo book were discovered flashed across his mind. He almost wished that he had tossed the thing overboard, for he had not had an opportunity of reading it and committing the salient facts to memory, and its recovery by the German authorities would mean not only that the information was lost to the British Admiralty, but that the crew of the Diomeda would be placed in a very awkward predicament.
"It's real rotten being hung up here," continued the American. "See, the sun is shining again." He pointed towards the single-barred window four feet above their heads, through which the sunshine was streaming brilliantly. Even as he spoke the shaft of light was suddenly obscured, and a dull whirring sound came from without.