The door was locked upon the prisoners, and the three officers hurried on deck. Q 171 was forging ahead, moving in wide circles around the sinking pirate craft. By this time the U-boat had dipped her stern. Waves were lapping along her deck as far as the after quick-firer. Her stem was correspondingly raised until the bow tubes were visible above water. Higher and higher rose the submarine's bows. Tons of water were flung into her hull through the open after-hatch. Compressed air was hissing loudly. Little rivulets of iridescent oil were forming on the surface. Occasionally interior fittings, giving way under the ever-increasing pressure, creaked and groaned to add to the discordant noises of the sinking craft. Then, with a shuddering movement, the U-boat slithered under the water. For a brief instant her bows stood almost on end. A column of water, forced by the terrific pressure through the fore-hatch, spurted a good fifty feet, ejecting with it a quantity of debris and oil. "_Bon voyage!_" exclaimed Wakefield. A turmoil of agitated water marked the spot where the submarine disappeared. For a full minute the maelstrom surged and swirled, then, overcome by the liberation of tons of heavy oil, the disturbed water died down, leaving in its place an ever-increasing patch of multi-hued colours. Forty fathoms down the submarine had made a permanent acquaintance with the bed of the North Sea. "Well, any luck?" inquired Morpeth, who, having left Ainslie in charge, had rejoined his unofficial guests in the ward-room. "What did you get out of von Preugfeld?" "Precious little," admitted Wakefield. "He tried to hedge. We'll have to confront him with some of his mutineering men." "I'll find out if there's any reference to the mysterious captain in this," said the R.N.R. skipper, holding up U 247's log-book. "Any of you fellows read the lingo?" "Sorry," replied Meredith. "You needn't be, old son," rejoined Morpeth. "I can't an' don't want to, although just now it would come in mighty handy. Some years back the Foul Anchor Line turned me down when I wanted a job as Second Officer on one of their crack boats because I couldn't speak German. They were carrying a lot of German passengers and South Americans at that time. Another fellow--Campbell was his name--got the billet 'cause he'd gained a first prize for German on a cadet training-ship. First trip he piled the old hooker aground off the entrance to Rio Harbour, 'and a dozen or more Huns got drowned." "So you were glad you didn't get the appointment after all?" asked Cumberleigh. "Rather," agreed Morpeth, with a laugh. "Not that I'd have put the ship aground. Guess I know that part of the South American coast too well. But, looking back on it, young Campbell was a patriot, only he didn't know it. We might have had another dozen Huns to fight. But to get back to business: here's this log wants looking into, and it's young Ainslie's trick. He's the Hun lingoist."