Everything was now in darkness, but by the presence of numbers of soldiers and seamen Hamerton concluded that one of the Zeppelins was about to be hauled out for a nocturnal flight. He wondered vaguely if he were to be an involuntary passenger.
A sliding door opened in the cliff, revealing a long passage lit at regular intervals with electric incandescent lights. A waft of hot, moist air greeted the Sub as he entered.
"By the right—march!" ordered the sergeant.
The tunnel was only wide enough to admit of two men walking abreast. Along the ground ran a narrow-gauge tram line. At every twenty-five yards or thereabouts was a niche, intended as a refuge for foot passengers upon the approach of any rolling stock. For the first hundred yards the tunnel was on the downgrade, then it was horizontal in direction. Overhead, and above the hollow tramp of his escort, the Sub could hear a dull, muffled roar: it was the sea. The tunnel, then, was passing under a portion of North Haven.
Hamerton calculated that he had gone quite a mile through the tunnel ere the upward gradient commenced. One hundred and twenty paces more and the prisoner and his escort were confronted by a steel door. On either side was a deep recess. In one of them stood a portly soldier in the uniform of the fortress artillery. Apparently he had already received his instructions, for, with a familiar nod to the non-commissioned officer in charge of the party, he unlocked and rolled back the sliding door.
For half a minute or so Hamerton could see nothing. The sudden transition from the well-lighted submarine tunnel to the blackness of the night temporarily deprived him of his sense of sight.
He gradually became aware that he was in a stone gallery open to the heavens, but additionally protected by mounds of earth and sand piled well above the level of the enclosing walls. To bind the soil, thorn bushes had been planted. These also served to screen the gallery from observation, while as a protection from shell-fire traverses had been provided.
Just above the summit of one part of the mound Hamerton could see a quaintly-shaped iron tower, the light from which was occulted every three seconds.
Now he knew exactly where he was. The opening of the tunnel was about a hundred yards north-west of the North Beacon of Sandinsel. Where the latest British Admiralty chart showed an expanse of sand covered at high water, his sense of vision told him that a vast extent of artificial ground had risen from the sea.
Another thing struck him in a very forcible manner: on either side of the gallery were hung rectangular steel plates, measuring roughly ten feet by six, and painted in a medley of colours. It was like the so-called "invisible" colouring on the guns and gun-shields of British fortifications, the idea being that at a distance the various hues would blend and form a neutral tint. But in this instance the metal plates were hinged at the top edge. They could be raised by means of levers, and thus form a V-shaped covering to the gallery, presumably as a protection from high-angle fire or from explosives dropped from a hostile airship.