As yet the Air Service Boys had not been engaged with any of the hostile planes, though most of the other Yankee pilots seemed to be having their hands full in meeting and repelling fierce attacks.

Both kept in readiness for work should their turn come, Tom manipulating the plane, and Jack working the rapid-fire gun which he had learned to handle so cleverly.

Strangely enough, Jack, as he looked, was reminded of a vast circus which he had once attended, and where tumblers, athletes, and trained animals were all performing in three rings at the same time.  He had found it utterly impossible to watch everything that went on, and remembered complaining lustily afterwards in consequence.

Now there were some eleven rings in all, besides what was taking place thousands of feet below, where the bombs had started to burst, tearing great gaps in the ground close to the bridge, and causing the water itself to gush upward like spouting geysers.

Lower still dropped the venturesome pilots guiding the destinies of the four huge bombers.  What chances they were taking, bent only on succeeding in the important task to which they had been assigned!

Jack knew he would never forget that dreadful crisis, no matter if he were allowed to live to the age of Methuselah; such an impression did it make upon his mind.

But their turn came at length, for in the dim light two big Gothas were discovered swinging in toward them as though bent on bringing about the destruction of the Yankee battleplane.

Jack forgot about what was taking place below, since all of his energies must now be directed toward beating off this double attack.  It had come to the point of self-preservation.  The Hun airmen were playing a prearranged game of hunting in couples.  While one made a feint at attacking, the other expected to take advantage of an exposure and inflict a fatal blow that would send the American aeroplane whirling to death.

Jack saw when the nearest plane opened fire.  The spitting flame told him this, for it darted out like the fiery tongue of a serpent.  He also realized that the bullets were cutting through space all around them; and a splinter striking his arm announced the fuselage of the plane had already been struck, showing the gunner had their range.

Then Jack began work on his own account, not meaning to let the fight become one-sided.  His duty was to pepper any of the enemy craft that came within range, regardless of consequences.  To Tom must be left the entire running of the plane motor, as well as the maneuvering that would form a part of the affray.

Heedless of what was taking place around them, the two chums devoted their attention to the task of baffling the designs of their two foes.  Wonderfully well did Tom manage his aerial steed.  They swung this way and that, dipped, rose, and cut corners in a dizzying fashion in the endeavor to confuse the aim of the Hun marksmen.