In consequence they had to cower under their shelter and wait until, later on, without warning, there would come loud shouts from the front, and when they craned their necks to catch the first glimpse of the foe shots from the rear would clean up that nest.
Morgan started with his signal work immediately after they had climbed to the proper altitude, where they might work without being in too great danger from the "Archies," or anti-aircraft guns.
As soon as he had a response, and knew that his directions were accurately noted, he announced the fact to Jack. They were then ready to begin all over and start "fishing" again.
It was very exciting work, and Jack Parmly gloried in it. Though he had to take additional chances in order to tempt the Hun gunners to betray their cunningly arranged coverts, there was also a satisfaction in knowing that by so doing he and his assistant were saving many precious lives of the infantry regiments down in the forest that had proved a graveyard for thousands.
A second time did they get a "bite." Again was the retreat conducted in the midst of a rattling volley, with hurtling missiles burning the air all around them, as well as beating a lively tattoo on the armored parts of their plane.
After that they flew higher, in the hope that some enterprising Boche flier, seeing their challenge, would come over to give them battle. For half an hour, they kept this up, and then, as they tempted forth no adversary, determined to drop down once more and root out a third nest before going in for the noonday meal.
"They're at it hammer and tongs to-day for fair!" called out Morgan, as he used his binoculars and picked out spots far below where there seemed to be open fighting going on. He could discover bodies of German troops being rushed forward and then falling back with decimated ranks before a fierce flame of shot and shell poured in by Yankee batteries.
"Getting desperate, that's what!" announced Jack, starting a dip that by stages would take them down once more into the dangerous quarter of treetops under which lurked the deadly foe with his thousands of rapid-fire guns.
Other planes were in sight here and there, carrying out similar tactics with more or less success, according to the daring of the pilot in tempting the Huns beyond their power to resist. Jack determined to pass further on and see what he could unearth in a new quarter.
What he and his chum had been talking of that very morning was still fresh in his mind. How he would like to discover one of those unusual nests where half a dozen or more gun crews lurked, ready to hold up that entire sector of the advancing line, so the American troops would be unable to reach their objective for that day at least.