The four-inch gun on the fo'c'sle barked. It was still dark enough for the flash to cast a lurid glow upon the set faces of the British officers, who stood by with their glasses ready to bear upon the flying torpedo-boat the moment the acrid fumes from the burnt cordite drifted clear of the bridge. The first shell struck the water close to the German vessel's port side, throwing up a column of water fifty feet in the air as it ricochetted and finally disappeared beneath the waves a mile or so ahead of the target. Fritz replied promptly. He must have fired; directly the flash of the "Audax's" bow gun was observed. The projectile screeched above the heads of the men on the bridge, seemingly so close that Barcroft involuntarily ducked. It was quite a different sensation from being potted at by "Archibalds." Up aloft the roar of the seaplane's engines and the rush of the wind practically overwhelmed the crash of the bursting shrapnel. This weird moaning, as the four-inch shell flew by, was somewhat disconcerting as far as Billy was concerned, while to heighten the effect a rending crash accompanied the passing of the projectile. "Our wireless top-hamper, dash it all!" exclaimed Aubyn, turning his head for a brief instant. "Starboard a little, quartermaster." The slight alteration of helm enabled the midship quick-firer on the starboard side to bear upon the enemy. The latter, evidently with the idea of dazzling the British destroyer, had switched on a searchlight mounted on a raised platform aft. Probably the Huns might have derived advantage from the rays, that still held their own against the increasing dawn, had not a well-directed shell from the "Audax" fo'c'sle gun blown searchlight, platform, and half a dozen men to smithereens. For the next ten minutes the adversaries were at it hammer and tongs. More than one shell got home on board the British craft, playing havoc with the after-funnel and deckfittings, while three badly wounded but still irrepressibly cheerful seamen were taken down below. The German craft was being severely punished. The speed had fallen off considerably, while she was on fire fore and aft, although the for'ard conflagration was quickly got under by her crew. By this time she bore broad on the British destroyer's bow, the range having decreased to 1,500 yards. Suddenly the Hun put her helm hard down. Either she saw that flight was no longer possible, or else her stern quick-firers had been knocked out, and she wished to bring her as yet unused guns to bear upon her foe. As she turned Aubyn saw through his binoculars a gleaming object shoot over the German craft's side, quickly followed by another. Both disappeared in a smother of foam beneath the waves. "Hard a-port!" he shouted, knowing full well that at that moment a couple of powerful Schwarzkopft torpedoes, propelled by superheated compressed air, were heading towards the "Audax" at a rate of forty to fifty miles an hour.