Just then a furious burst of quick-firing guns shook the air. With complete indifference to the fact that half a dozen of their own patrol-boats were hastening towards the hulk, the nearest batteries had opened fire. Fortunately the patrol-boats flung about and steamed off from the danger-zone as hard as their engines could go. "What are those fools firing at?" asked Huxtable, making way for the dripping form of the Sub as he descended the conning-tower hatchway. The Lieutenant-Commander knew that the batteries were not firing at the British craft, for she was quite invisible to the gunners. The shells were churning the water all around a dark object drifting with the current. It was the drum which Dick had thrown overboard. Picked up by the united glare of a dozen search-lights, ineffectually shelled by twenty or thirty quick-firers, the drum floated serenely towards the Bosphorus. Huxtable saw his chance and took it. So intent were the Turkish gun-layers upon blowing to pieces what they imagined to be the conning-tower of the hostile submarine, that neither they nor the men working the search-lights thought of anything else. Save for the shell-torn water in the immediate vicinity of the drifting drum, the sea was shrouded in intense darkness. "Cast off there!" ordered the Lieutenant-Commander; "diving stations." As soon as the two seamen had regained the interior of the vessel, hatches were closed and secured, and the submarine, with her conning-tower just awash, forged gently ahead against the stream. Then under the action of her horizontal rudders she quickly slipped beneath the surface and dived to sixty feet. "Here we are, sir," reported Dick, indicating on a chart the position of the submarine. "A course due east will take us towards the centre of the Bosphorus, and in the direction of Scutari." "Good!" ejaculated Huxtable. "Crosthwaite, you're a rattling good fellow. It was a smart idea of yours, slinging the drum overboard. It drew their fire splendidly. I don't suppose the rotten gun-layers have settled it yet." Dick said nothing in reply. Already he realized that his action had been done on the spur of the moment. The good result was simply a fluke. It seemed an absurd thing to have to confess that he had jettisoned the drum merely as an act of pique. Huxtable took his silence as a sign of modesty, and was still further impressed by the Sub's forethought.