By the aid of the appropriated German Naval Code Book, Q 171's skipper deciphered the signal. It was a peremptory request for the pseudo U-boat to make her number and thus proclaim her identity. This was easily done. A four letter hoist of bunting fluttered from Q 171's mast, giving the information that she was U 251 of the Imperial German Navy. "This is my prize," signalled the dog-in-the-manger Fritz. "I have good reasons for joining in the chase," was Morpeth's reply. During the lengthy exchange of flag messages, both boats had maintained a hot fire upon the tramp. From the genuine U-boat the result of Q 171's shells could not be observed. Had the Huns been able to do so, they would have expressed considerable surprise at their supposed consort's decidedly erratic gunnery; but in the heat of rivalry they became reckless. Almost imperceptibly, Q 171 lessened the distance between her and her prey. The tramp was two miles ahead, while barely half a mile separated the U-boat and the decoy. "Stand by the tubes!" ordered Morpeth, at the same time motioning to Wakefield and Meredith to step clear of the rails. Meredith felt a distinctly unpleasant sensation in his throat. Perspiration oozed from his forehead. Fascinated, he watched the alert faces of the men standing by the mechanism that was to lay bare the deadly torpedo-tubes. "Let her have it!" shouted Morpeth. With hardly a rumble, the dummy conning-tower rolled over the well-oiled rails, revealing the triple tubes trained abeam upon their prey. The next instant the glistening cigar-shaped missiles leapt over the side and disappeared in a welter of foam. Travelling at the rate of an express train under the impulse of small but powerful electric motors, the torpedoes took very little time to cover the intervening distance. So intent were the Huns at shelling the tramp that they failed to notice the tracks of the sinister weapons until, with an appalling roar, two of them exploded simultaneously and thirty yards apart against the U-boat's hull. Morpeth gave a grunt of satisfaction as he watched the tall column of water break and fall in a shower of smoke-mingled spray. "Simple--quite simple," he remarked; then, observing Meredith's white face, he clapped the young officer on the shoulder. "Cheer up!" he ejaculated. "Nothing to look white about the gills.... When you've been on the game as long as I have, and seen what an utter bounder Fritz is, you'll understand."