"Reverse the planes and try running the engine at full speed astern," suggested Tregarthen, now fully alive to the seriousness of their position. For a few seconds it seemed as if this manoeuvre would prove successful, though the water hissed through the tightly packed propeller shafting as the blades went astern. Then, with a decided swoop, the submarine returned to her muddy bed. "That's done it!" exclaimed Palmer, gloomily. "We've lost our slight reserve of buoyancy; don't say a word to discourage the men, but I fear it's all up." Gerald did not reply. Mechanically he pulled out his watch; it was twenty minutes over the hour. (_To be continued_) [Illustration: The four men threw themselves on the astonished foreigners, and a desperate conflict ensued.] [_See page_ 486. [Illustration: sixth instalment] BY PERCY F. WESTERMAN Author of "A Lad of Grit," etc. _ILLUSTRATED BY E. S. HODGSON_ [Illustration: chapter XXIII] CHAPTER XXIII THE CRIPPLED SUBMARINE "BETTER switch off the searchlight," said Gerald. "It's doing no good, and we must economise the air." "There's enough oxygen to last for two hours," observed Palmer; "but we had better try the motors full speed ahead once more. It can't do much harm, and the longer we remain inactive the deeper the boat will sink in the ooze." But beyond a slight pulsation of the hull the submarine remained in her hazardous position. "Look here," exclaimed Gerald's companion, hopefully, "why not close the torpedo compensating tank and discharge all the torpedoes? That will get rid of some of our gear." "What happens to the torpedoes when they have finished their run, provided they miss their mark?" asked Gerald. "If they have practice-heads they rise to the surface; if provided with war-heads they sink." "The same as our Whiteheads: the exhaustion of the compressed air actuating the propellers opens a valve that admits water into the air-chamber?" "That is so." "Then I'm afraid your plan is useless, for in expelling the torpedoes we are only getting rid of objects lighter than the weight of the water they displace." "You're right," assented Palmer, ruefully. "Beg pardon, sir," exclaimed one of the seamen, "but are we hitched up here for good?" "It looks like it," replied Palmer, almost brutally. "Then couldn't I go out by the air-lock--I am willing to risk it--and take a line up with me? We've nearly a hundred fathoms aboard." "Impossible, man; you would be crushed to death." "We ought to try something, sir; the oxygen seems to be giving out, and the mice are getting torpid." "I thought we had two hours' supply?" "So did I, sir, but something's wrong with the stuff." "We will have to rely on the oxygen helmets, then. Serve them out; it may prolong our lives a few hours, though I know not to what purpose."