At their heels came Herr Rix, the Leutnant of the submarine. He was beaming affably.
"Goot mornings!" he exclaimed. "You come mit me, den I show you how we blockade."
He led the way to the compartment in which the bowl of the supplementary periscope was placed. It was now broad daylight, and consequently the bowl showed a distinct image. A junior officer was standing by, but on seeing Rix approach he saluted and moved aside.
"Look!" exclaimed the Leutnant.
Both lads peered into the bowl. On its dull sides, an expanse of sea and sky was portrayed. Beyond that they could see nothing, until Rix called their attention to a small dark object.
"Englische sheep!" he declared. "Now you vos watch."
He touched a metal stud. Instantly an arrangement of telescopic lenses came into play within the tube of the periscope, with the result that a small portion of the view was greatly magnified upon the object card. It revealed a tramp of about nine hundred tons. She had a single funnel painted black, with two broad red bands; two stumpy masts, with derricks, and a lofty bridge and chart-house abaft the funnel. She was wall-sided. Her rusty hull was originally painted black. Here and there were squares of red lead, showing that her crew had been engaged in trying to smarten her up before she reached port. Aft, frayed and dirty with the smoke that poured from her funnel, floated the red ensign.
The submarine began to rise. Although she tilted abruptly, the image of the tramp steamer still remained upon the object bowl. By an ingenious arrangement, the lenses were constructed to compensate for any deviation of the tube of the periscope from the vertical. The lads could see the bows of the U-boat shaking clear of the water, throwing cascades of foam off on either side as the passing craft forged ahead at at least eighteen knots.
Now, for the first time, the skipper of the tramp saw the danger. He was a short, thick-set man, with white hair and an iron-grey moustache, and a face the colour of mahogany. For an instant he grasped the bridge-rails and looked towards the submarine, then gesticulated violently to the man at the wheel.
The spikes ran through the helmsman's hands, as he rapidly revolved the wheel actuating the steam steering-gear. The tramp swung hard to port, with the idea of baffling the momentarily expected torpedo.