"Stand by!" cautioned the Flight-Sub. "Keep cool. Do as well as you have already done, and everything will go like greased lightning."
Volplaning at an acute angle, the sea-plane swooped down upon her quarry. Shrapnel shells burst over, in front, behind, and underneath her. It seemed impossible that such a frail object could escape destruction.
At five hundred feet the Flight-Sub checked her downward course.
Two puffs of white smoke marked the points of explosion of the powerful bombs. One had fallen fifty yards short of the bridge; the other had burst almost at the junction of the railway lines.
Round spun the sea-plane. As she turned Ross could discern the second of the aerial raiders gliding down, while the third was still at a great altitude. Before the one in which Ross was flying could again soar over its target the second sea-plane had dropped three of her missiles. All fell close to the bridge. The work of demolition was accomplished, for when the smoke and dust cleared away the substantial fabric had been precipitated, a mass of twisted steel, into the canal.
[Illustration: "THE WORK OF DEMOLITION WAS ACCOMPLISHED"]
"Two more on the station and then we've finished," exclaimed the Flight-Sub. "Ready?"
He turned his head to watch the progress of the other sea-planes. One was still maintaining a terrific altitude, and showed no signs of making a volplane.
The other was nowhere to be seen. Perhaps it was as well that the midshipman had not noticed what had befallen her, for a few seconds previously a shrapnel shell had burst close underneath the chassis. The explosion had communicated itself to the remaining bombs, with the result that utter annihilation had overtaken the plucky British airmen in the moment of their triumph.
Ross's companion had witnessed the catastrophe. More, his trained eye had discerned half a dozen small specks in the western sky. Quickly he brought his binoculars to bear upon them. No mistake now; the specks revealed themselves as German aviatiks intent upon cutting off the retreat of the two remaining British air-craft.
Not until Ross had dropped the remaining bombs did his companion speak.
"We've a bit of a shooting match on," he announced. "Get that rifle ready. It's under the coaming on your right hand. Sight at three hundred yards, and let rip when I give the word."