As Don crawled forward to take his place behind the shielded shoulder of the machine gun, Fred stripped himself of the wireless paraphernalia to become mechanician while Jack and Andy gave all their time to the engines and the maneuvering. At the same time they climbed higher, maintaining the advantage which always is with the upper plane in aerial battle.

"Get ready, Don," Jack shouted, as the big machine swerved about and banked steeply for a sudden dive at the machine below.

Before the crew of the latter could even guess what was going to happen, much less get into position for firing their own gun, mounted forward, Don opened up with a hail of bullets which cut the lower left wing of the enemy machine in a dozen places and made her all the more difficult to maneuver or manage.

A skilled pilot was in charge of her, however, and even with this damage the giant plane wheeled gracefully, circling for an advantage which Jack and Andy refused to give. Up, up, up they went, cutting, crossing, swerving, always seeking for position.

And then like a flash Jack gave the order and they turned on the enemy. Again Don let go a fusillade that sounded like the rapid rat-a-tat of a great drum. It was another bull's eye, and one of the bullets apparently took the pilot in the right arm, for Fred, looking over, saw it drop limp at his side, while he frantically grasped at levers with his left hand, and said something sharply to another member of his crew.

The enemy, too, was firing his machine gun at every opportunity, but thus far the maneuvering of the American plane had been too sudden and swift to permit of anything like an aim, and the nearest shower of bullets went harmlessly by, several yards to the right.

Again Jack gave his engines all the petrol they would take, and there was another skyward spurt at hair-raising speed. No one direction was maintained for a full minute at a time, however, and even at that the enemy finally got a head-on opportunity and sent a charge that lodged several bullets in the outer fusilage. There was an instant change of course, and a few seconds later Don was given another opportunity to show what he knew about machine gun firing. He gave a most excellent accounting.

The rudder of the enemy plane was almost entirely shot away!

A skilful pilot may not necessarily regard that as a disaster, but already the pilot of the other machine was disabled, and the battle was raging so furiously that no opportunity offered for another of the crew to take his place.

With only one able hand and arm to work with the fellow did remarkably well, but he could not handle the giant plane successfully under such a handicap.

Even then, and in that desperate situation, Jack and his crew would have let up in mercy had not the enemy, in a long, circling dive again renewed the fire.

Jack nodded his head to Andy, and Fred, understanding the signal, got ready to do his part. They banked at a dangerous, nerve-racking angle, and then in a long, sweeping curve came down upon the already crippled machine which could not get out of the way.

Don loosened such a miniature artillery that two of the crew fell over either mortally wounded or killed outright. The firing never ceased, nor was the course of the plane changed until it was within fifty yards of the other machine and it seemed that a fatal collision was imminent.

The final volley tore both wings of the other plane so badly that she wavered, washed in the wind for a few seconds and then, as a spurt of flame appeared where fire had started from a leaking petrol tank, she settled into a swift and disastrous nose dive.

Don saw what happened; the others had too much to do in righting their own plane at that instant to pay attention to anything else. Jack and Andy had come literally as near as a hair losing control of their own plane in making the final attack which disposed of the other. As a matter of fact, had they not been such masters of their machine, all might have gone to the fate that the others found as the reward for their treacherous undertaking.

"What happened?" Jack asked of Don, when the machine again was under control. He had not realized that they had completely put the other machine out of business, and seemed somewhat surprised when, on looking about, he did not find it in pursuit, or dashing away on the defensive.

"It's all over," Don assured them. "You can take it easy now."

They did. They looked over the side of their own machine and saw what remained of a crushed and broken fusilage—just bits of wood and some strips of canvas—floating on the surface of the sea.

"They fell straight as an arrow, but in a tail dive, after that final attack," Don said. "It was really sickening to see them fall. It must have been four thousand feet at the least."

"Afire?" Jack asked.

"Yes, but completely out of business before the flames broke out," Don continued. "The pilot got a bullet in the right arm early in the mix-up, and I guess two of the others never knew what happened to them. When they struck it was with a splash like that sent up by a depth bomb. As a matter of fact, I didn't think anything connected with the machine would ever come to the surface again."

"Guess we'd better circle down and see if by chance any one of them should be alive and in sight," Jack suggested.

He changed course and they began a circling downward descent. Some fifty yards away from the floating dÉbris they made a landing. The sea was comparatively calm and they experienced little difficulty in settling on its surface without jolt, splash or damage. For several moments they lay there, looking intently at what remained of that which once had been Braizewell's powerful twin-motor biplane. There was not a sign of human life, not an evidence of anything indicating it.

"Don," said Jack, "for the purposes of a full report on this incident you had better note as exactly as possible the time and place where it occurred."

"Yes," Don responded, "I had thought of that, and I've already got my reckonings. It's merely a matter of recording them, which I'll do at once."

"Too bad for them," Jack said, with genuine sorrow in his voice. "But it was they or we. There was nothing else to it. They forced the issue and we had no alternative. I wonder who they were."

"I saw them all, at one time or another during the firing," Don then informed his companions. "But there was only one I thought I might have seen somewhere before. But when it was, or where, I'm at a loss to tell. As a matter of fact, I'm not at all certain that I ever saw him. But somehow his face seemed familiar."

"Well, we'd better be on our way," said Jack. "No use in staying around here. Those fellows probably went down so far that, even if they're not entangled in the wreckage, it's doubtful whether they ever would come up again."

"I've got it!" ejaculated Don abruptly.

"Keep it then," advised Andy, good-naturedly, despite the latest excitement they had been through.

"I've got it! That's it, surely," Don repeated again, gazing out abstractedly, as one will when absorbed in some recollection.

"Got what?" demanded Fred, impatiently. "Better get rid of it if you have, don't you think?"

"Eh?" Don looked at him blankly. "Oh, yes. Say! Do you know who that fellow was that I thought I recognized in that plane?"

"No, who?" asked Jack, keenly interested.

"Remember the day I came limping back with a badly crippled plane, after having been over the German lines, and was just able to make a descent within our own?"

"Sure!" they exclaimed, all at once.

"That was the fellow I had the battle with. I'm sure of it. I knew I'd seen him before, and that's when it was."

"Well, he's probably battling with Davy Jones now," said Andy soothingly. "You've had your revenge, and he'll never fight another air duel on this earth."