With her motors purring rhythmically and the pistons throbbing in perfect tune the seaplane swung round and settled in an easterly direction, the while climbing steadily. Behind her was the tail end of a nimbus; above, through a vast rift the stars twinkled in the cold sky; beneath, thousands of feet down, was the sea, its vicious, steep waves invisible in the kindly darkness.
Suddenly, from the enshrouding masses of cloud, a dark, symmetrically elongated shape shot rapidly into the starlight. It was a Zeppelin in full flight. Columns of smoke were issuing from her exhausts, but the throb of the seaplane's motors drowned the drone of her powerful engines.
"Good!" ejaculated Fuller, actuating the rudder bar with his feet and elevating the ailerons. "That's our bird. If they don't spot us before they gain that bank of clouds, she's ours."
Eagerly yet methodically Kirkwood brought the Lewis gun ready for action. It was to be the last resource in attack, to be used only if the seaplane failed to gain the aerial "weathergage"—a superior altitude to that of her bulky antagonist.
For the present the odds were level as regards speed. The seaplane's greater rate of flight was counterbalanced by the fact that she had to climb in order to get above her intended prey and drop a bomb upon the immense and fragile bulk of the Zeppelin's envelope.
And Fuller was achieving his object. Already Seaplane 445B was passing diagonally upwards through the raider's smoking trail, the oil tinged vapour from her exhaust pipes. Every moment tended to bring the protruding stern portion of the Zep, betwixt her crew and the steadily climbing aeroplane, thus diminishing the risk of detection.
Fuller was about to check the upward climb and overhaul his antagonist when the Zeppelin appeared almost to stand on end. The whole of her upper surface was exposed to the British airmen's view. Then, almost simultaneously the seaplane seemed to be following.
It was a form of optical delusion. She was still climbing steadily. The Zeppelin had spotted her small and dangerous foe. Dropping a quantity of ballast en bloc the airship shot vertically upward to a terrific height. It was this motion that had given Fuller the impression that the seaplane was dropping.
"She's twigged us!" he shouted through the voice tube. "Let her have it."
The A.P. promptly began to let loose a whole drum of ammunition. The Zeppelin was instantly enveloped in a cloud of smoke. Into the pall of vapour the Lewis gun pumped its nickel missiles, yet no crippled flaming fabric crashed helplessly to the surface of the sea.