And then, high up and at a vantage point, while below them hovered their photographing planes, the two young aviators beheld a curious sight.

In German-occupied territory, but on French soil, they saw near a railroad junction, where they were fairly well hidden in a camouflaged position, not one, but three monster Hun cannons. The guns looked more like gigantic cranes than like the accepted form of a great rifled piece of armament. The guns were so mounted that they could be run out on a small track at the moment of firing, and then propelled back again, like some of the disappearing cannon at Sandy Hook and other United States forts. Only the German guns advanced and retreated horizontally, while the usual method is vertically.

"We've discovered 'em! There they are!" cried Tom, but of course he could not hear his own voice above the roar of his motor. But he knew that he and Jack were over the very spot where the night before they had seen the colored flares from the great guns.

And they had, indeed, by a most lucky chance, located the big German guns, for there were three of them. They were placed almost midway between the railroad station of Crepyen-Lannois and the two forts known as "Joy Hills," forts which had fallen into German hands. There were two railroad spur lines from the station, and on these the heavy guns were moved to position to fire, and then run back again. Other spur lines were under course of construction, Jack and Tom, as well as the other airmen, could observe, indicating that other guns were to be mounted, perhaps to take the place of some that might be destroyed.

As a matter of fact, as was learned later, there were but two guns in service at this time, one of the three having burst.[1]

[Footnote 1: While of course this story is fiction, the description given above of the great guns and their method of firing and concealment is strictly in accord with the facts, and made from a sight of aeroplane photographs taken by the French, and from an official report, published April 26, 1918, by Deputy Charles Leboucq of the Department of the Seine.]

Even as the French squadron came hovering over the place where the German monster guns were placed, the advance of Tom, Jack and their comrades being disputed by the Huns, one of the super-guns was run out to fire on its specially constructed platform.

That this should be done in the very faces of the French was probably accounted for by the fact that the Germans were taken by surprise. It took some little time to arrange for firing one of the big cannons, and it was probably too late, after the French airmen were hovering above it, to get word to the crew not to discharge it.

As it happened, Tom and Jack, with Boughton, who had kept pace with them, witnessed the firing of the big gun. As it was discharged, ten other heavy guns, but, of course, of much less range, were fired off, being discharged as one to cover the report of the giant mortar. And at the same time dense clouds of smoke were sent up from surrounding hills, in an endeavor to screen the big gun from aeroplane observation. But it was too late.

In another moment, and even as the echoes of the reports of the ten cannons and the big gun were rumbling, the bombing machine of the French came up and began to drop explosives on the spot. At the same time word of the location of the great cannon was wirelessed back to the camp, and there began a devastating fire on the guns that had been, and were even then, bombarding Paris.

CHAPTER XXII

OVER THE RHINE

It was a battle of the air and on the ground at the same time. From above the French, American and British airmen were dropping tons of explosives on the emplacements of the big guns and on the railway spurs that brought them to the firing points. It might seem an easy matter for an airship flying over a place to drop an explosive bomb on it and destroy it. But, on the contrary, it is very difficult.

The bombing plane must be constantly on the move, and it takes a pretty good eye to calculate the distance from a great height sufficiently well to make a direct hit.

But a certain percentage of the bombs find their mark, and they did in this case. Tom and Jack, as well as the other scouts, looking down from their planes, saw fountains of brown earth being tossed into the air as the French bombs exploded. At the same time the photographers in the other planes were making pictures of the guns and their location.

They were hindered in this not only by the shooting of the Germans from below, who were working their anti-aircraft guns to their capacity, but by screens of smoke clouds, which were emitted by a special apparatus to hide the big guns. At the same time other cannons were being fired to disguise the sound from the immense long-range weapon, but this was of little effect, now that the location had been discovered.

Meanwhile a score or more of the Hun planes appeared in the air. They had taken flight as soon as their pilots saw the squadron of enemy machines approaching, and were eager, this time, to give battle.

"Our work's being cut out for us," murmured Tom, as he steered his machine to engage a German who seemed eager for the fray. Tom sent a spray of bullets at his enemy, and was fired at in turn. He knew his craft had been hit several times, but he did not think it was seriously damaged.

Jack, too, as he could tell by a quick glance, was also engaged with a German, but Tom had no time then to bestow on mere observation. His antagonist was a desperate Hun, bent on the utter destruction of Tom's machine. They came to closer quarters.

Down below the fighting was growing more furious. It was in the form of an artillery duel. For now the French observation machines were wirelessing back the range, and French sh.e.l.ls were falling very near the big guns.

The heavy guns, in modern warfare, are placed miles away from the objects they wish to hit, and the only way to know where the targets are is by aeroplane observation. When the guns are ready to fire one of the artillery control planes goes up over the enemy's territory. Of course it is the object of the enemy to drive it away if possible.

But, hovering in the air, the observer in the double-motored machine notes the effect of the first shot from his side's cannon. If it goes beyond the mark he so signals by wireless. If it falls short he sends another signal. Thus the range is corrected, and finally he sees that the big sh.e.l.ls are landing just where they are needed to destroy a battery, or whatever is the object aimed at. The observation complete, the machine goes back over its own lines--if the Germans let it.

This sort of work was going on below them while Tom, Jack and the others in the Nieuports were engaging in mortal combat with the Hun fliers.

Some of the heavy French sh.e.l.ls fell beyond the emplacements of the big guns, and others were short. The observers quickly made corrections by wireless for the gunners. Tom Raymond, after a desperate swoop at his antagonist, sent him down in flames, and then, seeking another to engage, at the same time wondering how Jack had fared, the young aviator looked down and saw one of the largest of the French sh.e.l.ls fall directly at the side of the foremost of the three German giant cannons.

There was a terrific explosion. Of course, Tom could not hear it because of his height and the noise his motor was making, but he could see what happened. A great breach was made in the long barrel of the German gun, and its emplacement was wrecked, while the men who had been swarming about the place like ants seemed to melt into the earth. They were blotted out.

"One gone!" exclaimed Tom grimly. And then he noted that the other two guns had been withdrawn beneath the camouflage. They were no longer in sight, and hitting them was a question of chance.

Still the French batteries kept up their fire, hoping to make another hit, but it would be a matter of mere luck now, for the guns were out of observation.

The airmen observers, however, still had a general idea of where the super-weapons were, and the French gunners continued to send over a rain of sh.e.l.ls, while the bombing machines, save one that had been destroyed by the German fire, kept dropping high explosives in the neighborhood.

"The place will be badly chewed up, at any rate," mused Tom.

He glanced in the direction where he had last seen Jack, and to his horror saw his chum's machine start downward in a spinning nose dive.

"I wonder if they've got him, or if he's doing that to fool 'em,"

thought Tom. As he was temporarily free from attack at that instant he started toward his friend. Hovering over him, and spraying bullets at Jack, was a German machine, and Tom realized that this fighter might have injured, or even killed, Jack.

"Well, I'll settle your hash, anyhow!" grimly muttered the young birdman to himself. He sailed straight for the Hun, who had not yet seen him, and then Tom opened fire. It was too late for the German to turn to engage his second antagonist, and Tom saw the look of hopelessness on his face as the bullets crashed into his machine, sending it down a wreck.

"So much for poor old Jack!" cried Tom.

They were well over the German lines now, and the fight was going against the French. That is, they were being outnumbered by the Hun planes, which were numerous in the air. But the French had accomplished their desperate mission. One of the German guns was out of commission, and perhaps others, while the location had been made "considerably unhealthy," as Boughton expressed it afterward.

It was time for the French to retire, and those of their machines that were able prepared to do this. But Tom was going to see first what happened to Jack before he returned to his lines.

"He may be spinning down, intending to get out of a bad sc.r.a.pe that way, and then straighten for a flight toward home," mused Tom. "Or he may be--"

But he did not finish the sentence.

There was but one way for Tom to be near Jack when the latter landed--if such was to be his fate--and to give him help, provided he was alive.

And that was for Tom himself to go down in a spinning nose dive, which is the speediest method by which a plane can descend. But there is great danger that the terrific speed may tear the wings from the machine.

"I'm going to risk it, though," decided Tom.

Down and down he spun, and as he looked; he became aware, to his joy, that Jack had his machine under some control.

"He isn't dead yet, by any means," thought Tom. "But he may be hurt. I wonder if he can make a good landing? If he does it will be inside the German lines, though, and then--"

But Tom never faltered. He must rescue his chum, or attempt to, at all hazards.

Down went both machines, Jack's in the lead, and then, to his joy, Tom saw his friend bring the machine on a level keel again and prepare to make a landing. This was in a rather lonely spot, but already, in the distance, as Tom could note from his elevated position, Germans were hurrying toward the place, ready to capture the French machine.

"If he's alive I'll save him!" declared Tom. "My machine will carry double in a pinch, but he'll have to ride on the engine hood."

Tom was going to take a desperate chance, but one that has been duplicated and equalled more than once in the present war. He was going to descend as near Jack's wrecked machine as he could, pick up his chum, and trust to luck to getting off again before the Germans could arrive.

That Jack was once more master of his craft became evident to his friend. For the Nieuport was slowing down and Jack was making ready for as good a landing as possible under the circ.u.mstances. It was plain, however, that his machine was damaged in some way, or he would have gone on flying toward his own lines.

Tom saw his chum drop to the ground, and then saw him quickly climb out of his seat, loosing the strap that held him in. By this time other German planes were swooping toward the place, and a squad of cavalry was also galloping toward it.