Dave had already reasoned out the probable course of the neutral country's freighter in the last hour before he had overhauled it. As the mine-sweeper slowly came abreast, Darrin, a megaphone at his lips, shouted an order for the course to be taken by his small helper, and added:
"Sweep thoroughly, and try to find some mines near by."
"Aye, aye, sir."
Within fifteen minutes a distant whistle came up from the fog.
"They've picked up one mine," Darrin announced.
Ten minutes later the sweeper's signal whistle was repeated.
"Two mines," he added, and the "Olga's" skipper shivered slightly.
Twenty minutes later came a whistle that was barely heard.
"Three mines," clicked Dave, and ordered the recall sounded, to be by direction signals at minute intervals.
"You make dot noise too much den have us all torpedoed yet," protested the "Olga's" skipper.