As if running for a challenge cup, the ex-bank clerk and the former public schoolboy tore aft. They knew their job: to release the deadly depth charges and to stand by the firing key, by means of which the electric circuit was completed and the explosive detonated. All out, the M.-L. made straight for her intended victim, her quick-firer giving the U-boat a preliminary show by way of encouragement. The shell missed the conning-tower by inches. Before the breech-block could be opened, the still-smoking cylinder ejected and another charge inserted, the U-boat dived so abruptly that for a few seconds her rudders and twin-screws were clear of the water. "Starboard . . . at that!" Branscombe, his eyes fixed upon the surface-swell of the now submerged pirate, waited until the M.-L. was crossing the path of the frantically-diving Hun. "Let go aft!" With a smother of foam, the metal canister toppled from its cradle into the milk-white wake of the swiftly-moving M.-L. The drum, on which the insulated wire was wound, began to revolve rapidly as fathom after fathom was paid out. The Sub stepped from the wheel-house and raised his hand. Then, with a quick decisive motion, he brought it down to his side. At the signal, the key of the firing-battery was pressed home. "Bon voyage, Fritz!" murmured Branscombe, as with an ear-splitting report a column of mingled smoke and foam rose quite two hundred feet into the air. With her helm hard a-port the M.-L. circled rapidly to starboard, and, steadying, passed at slow speed through the patch of agitated water. One of the crew made ready to let go the mark-buoy to indicate the position of the sunken U-boat. He waited for the order, but Branscombe gave no word of command. Gripping the stanchion-wires, the Sub leant over the side and watched. Then his look of elation gave place to an expression of acute disappointment--like that of a needy man who picks up from the gutter what he imagined to be a "Bradbury", only to find that it is a wrapper of a packet of tobacco. There was nothing--absolutely nothing--to indicate that the depth charge had carried out its pre-ordained mission. Not a vestige of oil floated on the surface of the sea. There were dead fish in hundreds, killed by the terrific explosion, but not a scrap of debris that by any stretch of the imagination could be attributed to the strafed U-boat. Up pelted M.-L. 4453, closely followed by No. 4454. The skipper of the former raised a megaphone to his lips. "Any luck?" he asked cheerfully. "'Fraid not," shouted Guy, trying to hide his chagrin. "Hard lines," was the sympathetic rejoinder. "Yes, my luck's out this time," soliloquized Branscombe, as he gave orders for the former course to be resumed. "I wish to goodness I'd blown the beastly thing to bits."