Presently the British seaplane's Lewis gun barked. It was evident that the machine was running uncontrolled, as she was wobbling considerably. Barcroft was now near enough to see what had happened. There was just time for a brief glance, for his plane was approaching the on-coming Huns at an aggregate speed of nearly 180 miles an hour.
There was no sign of Gregory, but Fuller, abandoning the joy-stick, had climbed into the observer's seat in order to work the automatic gun. This he did so successfully that within five seconds of the weapon opening fire one of the Fokkers crashed earthwards, completely out of action. Then the British gun was silent.
This was all that Barcroft could see as far as Fuller was concerned. He had devoted all his attention to the double-fuselaged craft.
While Kirkwood was letting loose a drum of ammunition from the Lewis gun Barcroft employed his usual tactics. He steered straight for his antagonist. If the gun failed to do its work in time, and if the Hun pilot's nerves did not desert him, the result would be a rending crash in mid-air as the two swift-moving craft collided. The interlocked wreckage, a mass of flame, would drop like a firebrand to earth—a swift yet terrible death for friend and foe alike. But Billy knew how the odds were against such a mutual catastrophe. The Hun, if he managed to avoid the stream of bullets, was not likely to "stand up" to the resistless onrush of the British seaplane.
Suddenly the double-fuselaged biplane nosedived. Only just in time did Barcroft tilt the ailerons, for the seaplane literally scraped the tail of his vertically-descending foe. For nearly a thousand feet the machine "plumbed," then like a silvery dart it flattened out.
"Old trick, Fritz," muttered Barcroft. "Well, you've lost your altitude advantage. I'll renew your acquaintance later."
The flight-sub knew that some minutes must elapse before the double-fuselaged machine could climb to renew the encounter. During that interval he had time to devote his attention to the remaining Fokker that, following Fuller with deadly persistence, was firing the while but receiving no reply from the British craft.
Already Fuller was a couple of miles away. His antagonist was gaining slightly. It seemed remarkable that with such a prodigious outlay of ammunition the Huns had not succeeded in strafing their quarry.
Suddenly Fuller's seaplane dipped. Barcroft gave vent to an involuntary groan, but the next instant he wanted to cheer, for his chum had looped the loop two or three times and was now heading in the opposite direction.
"I see the move," thought Barcroft. "He's luring Fritz towards us."
The two seaplanes passed one another at less than a hundred yards. Fuller raised his arm by way of greeting as they swept by. As he did so shreds of canvas flew from the lower plane, and dipping abruptly the crippled machine dropped, lurching hideously as it did so.
Almost simultaneously the Hun pilot of the Fokker collapsed across the decking of the fuselage. The machine, no longer under control, swayed through a distance of nearly a quarter of a mile, and then, tilting obliquely, began a terrific tail spin that ended in a jumble of wreckage on the unsympathetic soil of Belgium.
"Now for the double bus," muttered Billy. "The Huns will pay dearly for strafing poor old John."
But the remaining aeroplane of the two had had enough, for, seeing the British seaplane swooping down to engage upon round two, she promptly sought safety in flight.
Pursuit, Barcroft knew, was futile. Not only was the fugitive going in an easterly direction, which meant that had Billy held on in chase he would be lured further and further away from his floating base, but the Hun machine was more powerfully engined and possessed an undoubted superiority of speed.
"By Jove!" shouted the A.P. "Fuller's planing down. He's got the old bus under control of sorts."
The flight-sub looked downwards. A small rectangular patch of grey eighteen hundred feet down confirmed the truth of Kirkwood's statement. The injured seaplane was volplaning in wide circles. Her pilot was about to make an involuntary landing. This, in itself, was a highly dangerous performance, as the floats were very unsatisfactory landingskids. It was a hundred chances to one that the seaplane would bump hard and collapse, pinning the pilot under the wreckage. Even if Fuller escaped with his life or without broken limbs, he was confronted with the additional danger of being made a prisoner.
Without a moment's delay Barcroft switched off the ignition and commenced a volplane. At least he would be able to discover whether his chum was able to make a safe landing. Beyond that—
"Good old Fuller!" almost yelled the A.P. "He's spotted a canal. I see his move—artful bounder!"
Running in a direction approximately east and west was a long stretch of artificial water. The straightness of its course showed that it was not a river. It was bordered on either side by a broad tow-path, which in turn was fringed by a line of poplars. With the exception of a string of barges being towed down by a small tug (and they were nearly two miles away) the canal looked deserted.
It was for this expanse of water that Fuller was making. Provided there was sufficient width for the extreme breadth of his wing spread and a margin to boot, there was little doubt of the experienced flight-lieutenant's ability to make a safe descent.
"He's done it!" announced Kirkwood.
"If he has managed it there is no reason why we shouldn't," thought Barcroft grimly. "Stand by, old man; we'll shove down and pick him up."
The canal appeared to expand in size in order to meet the descending seaplane. It required all the skill and nerve at the youthful pilot's command to carry out his desperate plan. An error of a few feet to right or left meant irreparable damage to the frail craft and failure of his devoted efforts on behalf of his stranded friend.
With admirable judgment Billy brought his "bus" down, making a fine "landing" on the surface of the canal at a distance of less than a hundred yards from the crippled aircraft, Then, drifting gently, the seaplane brought up alongside the bank, with one of her floats rubbing against the edge of the tow-path.
"Nip out and hold her on, old man!" exclaimed Billy.
The A.P. obeyed promptly. Fortunately this required little or no effort, for the thick-set though leafless trees broke the force of what wind there was.
Barcroft quickly followed Kirkwood to the bank. Already Fuller had got ashore, and was preparing to destroy his machine when, to his utter astonishment, he had seen another seaplane skim over his head and alight at a short distance off.
Running by the path Billy approached the lieutenant.
"Come along, old man!" he said hurriedly. "There's no time to be lost. We'll give you a lift in our bus back to the old 'Hippo.'"
"Thanks," replied Fuller coolly. "What's the hurry? No Huns in sight. I'll do this job properly."
The odour of petrol vapour wafted to Barcroft's nostrils. Fuller had allowed the spirit to escape from the tank, and was engaged in wrapping a piece of oil-soaked paper round a stone.
"No explosives left, I hope?" asked Billy. "None except the petrol," replied Fuller. "That's explosive enough, I reckon, for this job. No, I dropped all my plums over Aerschot. Gregory's gone (s'pose you can see that for yourself?); shot through the head; he gave a sort of leap—he wasn't strapped in, you'll understand—and flopped right over the fuselage."
"You've been strafed!" exclaimed Barcroft, for Fuller's quick sentences, coupled with the fact that he winced frequently, pointed to that.
"The child is correct," agreed the flight-lieutenant. "Machine-gun bullet clean through the left arm. It stings a bit, but nothing much. No, don't trouble about it now. It'll keep. Now for a blaze."
Striking a match he set light to the oiled paper and tossed the flaming missile into the fuselage of the doomed seaplane. With a rush of air and a lurid flare the petrol vapour caught. In an instant the machine was enveloped in fire.