"What's that?" enquired the Hon. Derek, without turning his face from the vision of his expected victim. "Vessel to starboard? Nothing in sight up-topsides, by Jove. All right, carry on. We'll tackle our Zeppelin friend first of all, and then see what it is that's worrying you." Fordyce could not but admire his skipper's coolness. Somewhere within audible distance of R19 was another under-water craft, hostile, no doubt, and intent upon the British submarine's destruction, unless--jealous thought!--it were another of the E Class stalking the crippled airship. Whichever it might be, the Hon. Derek was resolved to leave her severely alone, risking a torpedo or being rammed until he had had a smack at the huge gas-bag. "Up with her!" ordered the Lieutenant-Commander. There was no necessity to blow the ballast-tanks. R19 had been kept to 19 feet solely by the action of the deflected horizontal diving rudders. Like an ungainly porpoise the submarine "broke surface", and the guns' crews raced up the ladders and through the now open hatchways. At an angle of 30 degrees from the perpendicular, and at a bare 2000-feet altitude, was the Zeppelin, presenting a splendid target. Proceeding in the same direction as the submarine, she was evidently unaware of the latter's presence, for not a shot came from the quick-firers mounted in her nacelles, nor did an aerial torpedo hurtle downwards towards the British craft. No. 3 quick-firer--the one immediately in the wake of the conning-tower--was the first to open fire. Ere the haze of the burning cordite had drifted aft, the smoke from the bursting shell mushroomed close to the huge envelope. It seemed impossible that the fragile fabric could hope to escape the terrific impact. Another and another shell sped from the submarine's guns. Still the Zeppelin held on. Then a cloud of black smoke hid the target from the gun-layers' eyes. The men raised a rousing cheer. "Got her, by the bosun's cat!" shouted a bluejacket, unmindful of everything in his excitement and delirious joy. But the cat of the afore-mentioned warrant officer must have been a bad mouser, for when the smoke drifted away the Zeppelin was 12,000 or 14,000 feet in the air. Under cover of the camouflage--for it was smoke purposely emitted in order to screen her movements--the air-ship had thrown out a large quantity of ballast, and had shot vertically upwards out of effective range. Even as they watched, the bluejackets were aware that R19 was porting helm. Circling eight points to starboard, she headed straight for a pole-like object forging ahead through the crested waves--the periscope of a U-boat that was either about to "break surface" or else to let fly a torpedo at the British submarine. CHAPTER VII A Double Bag