"We'd best turn back to camp," Schnitzel at last suggested. "It's twenty after three, and we must be almost a mile from headquarters. I want to fix up my pack before we start." The exploring party had left their heavy packs and equipment in charge of a comrade. They carried on their stroll only their haversacks containing their supper and breakfast ration, two thick sandwiches apiece. Until dugout shelters were reached the next morning, they would have no more hot food. Nothing that required cooking would be given them on this last march except hot coffee. Now, so close to the German lines, the cook wagons would be temporarily closed. Bits of food or sparks dropped in the road might also serve to inform the enemy that Uncle Sam's Boys were nearing the front. About to retrace their steps, the five Khaki Boys were suddenly brought to a sudden standstill by a loud cry from Ignace. "Look you!" he exclaimed, pointing upward. "So is it the fight by the air!" Instantly turning their eyes skyward, the group saw high above them an aeroplane cutting wild circles in the air. Around it little puffs of white smoke were continually bursting. As each puff burst, a peculiar "plopping" could be heard, though dully. The plane itself was up too high for the watchers to tell much about it. Besides, they were not familiar enough with the various types of aeroplanes used by the Allies and the Huns to be able to distinguish to which side it belonged. "It must be a French or an English plane, and the Boches are peppering it with anti-aircraft shells," surmised Bob, ever ready to theorize on whatever chanced to meet his gaze. "You're wrong, old man. It's a Boche plane, and the Allied guns are after it." Schnitzel's correction was uttered with a quiet positiveness that brought instant questions of, "How do you know?" "Who put you wise?" "What makes you so sure of that?" "Oh, I've been finding out all I could about anti-aircraft guns, batteries, shells and all that," Schnitzel answered. "I worked in a gun plant, you know, before I enlisted. I've told you that. Machine guns were its specialty, but I learned a lot about other kinds of guns, too. I put in a request for Artillery when I enlisted, but I landed in Infantry instead. I was pretty sore about it at first, but I soon got over it. "Just the same," he went on, "I've still a hankering after the big guns. I've been asking questions right and left ever since we came over. Back in England at the rest camp I met a Tommy who'd been in artillery since the war began. He'd done his bit, and lost an eye, so he was back to Blighty for good. He told me a lot of interesting stuff about guns. He said the Allied anti-aircraft shells showed white smoke when they exploded, and the Boche anti-shells showed black. So there you are. If what he said was so, and I'm sure it was, that's an Allied battery shelling a Boche plane."