Well before the time of his jailers' visit he withdrew the steel and hid it in the under side of the bed, replaced the leg of the stool, and resigned himself to a period of inaction.
As soon as it became dark the searchlights were switched on. Hamerton could see the giant beams travel slowly across the sky, although most of the searchlights were trained to sweep the surface of the sea. At frequent intervals the bark of quick-firers shook the solid building. A night attack, one of the frequent attempts upon Heligoland by the Borkum flotilla of destroyers, was in progress. Similar manoeuvres were of almost nightly occurrence.
The detonations of the ordnance were of immense service to Hamerton. He could begin operations with less chance of being detected, for the rasping of the steel point against the cement was inaudible during the firing.
Nevertheless, it was slow work chipping out minute particles of the stoutly resisting substance. Frequently he paused to gather up a handful of the debris and hurl it out of the window. In two hours he had cut out the cement to a depth of two inches round the fairly large slab which he had fruitlessly attacked with the fragment of the broken earthenware plate.
Shortly after eleven o'clock the firing suddenly ceased, although the searchlights were still flashing across the sky. There was now more need for caution. The Sub stuck grimly to his task, pouring water into the little rectangular trench in order to deaden the sound of the steel. Several times he had to "knock off" in order to reply to a signalled message from Detroit.
"You are not communicative to-night," tapped the latter.
"No, not in the sense you mean," replied the Sub. He would dearly have liked to inform the American of the work he was undertaking, but, fearing that the conversation was possibly being listened to by a third person, he refrained. "I'm dead tired," he added.
"Of doing nothing?" asked Detroit.
Hamerton looked at his bruised and blistered hands and smiled grimly. The irony of the American's question tickled him.
Far into the night he toiled. The stone showed no sign of loosening in its bed. Again and again he ground the edge of the piece of steel and attacked the stubborn cement, which seemed to possess the toughness of iron.