So great was the distress of the Hun forces that it was believed Marshal Foch had laid a vast trap and was using the fresh and enthusiastic Yankees to drive a dividing wedge between Ludendorff’s two armies, when a colossal surrender must inevitably follow.

The whole world now knows that this complete break-up of the Teutons was avoided solely by their demand for an armistice, with an agreement on terms that were virtually a surrender—­absolute in connection with their navy.

Tom and Jack had displayed considerable ability in carrying out their work, and could no longer be regarded as novices.  Each of them had for some time been anticipating promotion, and hoped to return home with the rank of lieutenant at least.

They had been entrusted with a number of especially dangerous missions, and had met with considerable success in putting these through.  Like most other ambitious young fliers, they hoped soon to merit the title of “ace,” when they could point to at least six proven victories over rival pilots, with that number of planes sent down in combat.

On the present occasion they had sallied out “looking for trouble,” as Jack put it; which, in so many words, meant daring any Hun flier to meet them and engage in a duel among the clouds.

Other planes they could see cruising toward the northwest, and also flying in an easterly direction; but as a rule these bore signs of being Allies’ machines, and in all probability had Yankee pilots manning them.

Apparently the Hun airmen were otherwise employed.  They seemed to prefer venturing out after nightfall, gathering in force, and often taking a strange satisfaction in bombing some Red Cross hospital, where frequently their own wounded were being treated alongside the American doughboys.

During the weeks that the Americans were battling in the great Argonne Forest the two Air Service Boys had contributed to the best of their ability to each daily drive.  Again and again had they taken part in such dangerous work as fell to the portion of the aviators.  Their activities at that time are set down in the fifth volume of this series, entitled:  “Air Service Boys Flying For Victory.”

Frequently they had found themselves in serious trouble, and their escapes were both numerous and thrilling.  Through it all they had been highly favored, since neither of them had thus far met with a serious accident.  Numbers of their comrades had been registered as “missing,” or were known to have been shot down and lost.

It was no unusual thing a few days after a flier had gone out and failed to return at evening, for a Hun pilot to sail over and drop a note telling that he had fallen in combat, and was buried at a certain place with his grave so marked that it could be easily found.

There seemed to be a vein of old-time chivalry among the German airmen even up to the very last, such as had not marked any other branch of their fighting forces, certainly not the navy.  And the Americans made it a point to return this courtesy whenever an opportunity arose.