The pain was acute, but for the time being Hamerton paid slight heed to it. His fingers, numbed by the shock, were powerless to reopen the heavy metal cover.
Yet no hands grasped his, no hoarse voice demanded his surrender. He looked down over his shoulder, and the cause of the sudden light became apparent. In his descent he had touched a switch that was conveniently fixed to a steel upright supporting the dome. Perfect silence reigned in the place, whatever it might be.
Disengaging his fingers, Hamerton descended the remaining rungs of the ladder. He realized that the accident was a blessing in disguise, for the slamming-to of the cover plate had effectually screened all light from within. Previous to this some light might have escaped, unless intercepted by his body as he crawled through the manhole.
The chamber was almost entirely occupied by the mountings of an enormous gun. The muzzle of the weapon disappeared behind a close-fitting steel shield that effectually prevented any light from being seen from seaward. It also prevented the Sub from approximately measuring the length of the gun, but upon opening the breech block he was able to conclude that the bore was not less than fifteen or sixteen inches. The gun and its enclosed shield were of a disappearing nature, while the loading tray was so constructed that the huge weapon could be served in any position.
At the rear of the loading tray was another opening that upon investigation Hamerton found to lead to the mechanism room for elevating the gun and its mounting. Here, too, was the opening to a subterranean passage, but the door was locked. Judging by the tram rails, the Sub concluded that it communicated with the principal magazine, that must be situated, deep under the ground, somewhere in the centre of the island.
"The whole blessed island is honeycombed," he exclaimed. "It's a second Gibraltar, only much more heavily armed. What a nut for us to crack when the time comes!"
Realizing that it was about time to rejoin his companion, the Sub ascended the ladder, switched off the light, and cautiously removed the slide. The exertion told him how painful his fingers had become, while he was forcibly reminded of his fall by a peculiar numbing sensation in the nape of his neck.
Without, the monotonous click of the signal lamp in the hut still continued. The searchlight was now switched on, but the operators had made a bad contact of the carbons, for the latter were hissing and spluttering abominably. This was in the Sub's favour, for the attention of the engineers was directed upon their work, and the noise of the searchlights effectually drowned the slight scraping sound that Hamerton made as he attempted to scale the walls of the gun pit.
Thrice he essayed the task. Under ordinary conditions a six-foot wall would have presented no great obstacle, but his strength had been sapped by his two accidents.
Round the edge of the dome he crept, till at the part facing the sea he discovered an iron ladder sunk in a recess in the wall, so as not to impede the raising of the armoured gun shield and its contents.