Consequently they would be apt to assemble a flotilla of fighting planes in that vicinity, ready to soar aloft and give furious battle to any Allied squadron venturesome enough to make the attempt at destruction.

If the blowing up of the bridge could only be accomplished, the sacrifice of a few planes with their crews might be counted a cheap price to pay for the great benefits reaped.

The minutes passed, and all the while the raiders were drawing nearer and nearer their intended goal.  Every pilot and observer in that squadron had been carefully selected with a view to his fitness for the gigantic task that had been laid out for accomplishment.

There would be no hesitation when the eventful moment came, since none was present save those who had been tried in the furnace of battle and found to be fine gold, eighteen carat pure.  Such a thing as flinching when the test came was not to be considered; they would carry through their appointed tasks or fall while in the endeavor, paying the price the airman has ever had dangled before his eyes.

Jack was using his night-glass, and he now broke out with a cry.

“We must be getting close to the bridge, Tom!  I can see flickering lights darting about, and I believe they must be planes rushing up into the air!”

“Like as not they’ve been warned of our coming by the row we’re making,” replied the pilot, in a shout.  “Then again those Huns along the line would send word back, for they must know what we’re aiming at.  It’s all the same to us.  We came out after action, and we’d be terribly disappointed if we didn’t get a lot of it.”

Then came signals from the leading plane.  Closer formation was the rule from that time forward, since the bombers must be amply protected in order to allow their gunners an opportunity to get to work with those frightful explosives and hurl them at the place where the bridge was supposed to lie.

Both boys began to feel their pulses thrill with eagerness, as well as excitement.  Looking down, Jack could detect moving lights, the source of which he could only speculate upon.  Then came a flash which must mark the discharge of the first anti-aircraft gun.  The enemy was showing exceeding nervousness, for as yet the leading American plane could not be anywhere within range.

With the burst of shrapnel there came a realization that the gunners below were only trying to get their range.  The whole pack would break loose in another minute or less; but Jack had reason to believe their altitude was such as to render the fusillade harmless.

Then down below he saw a sudden brilliant flash.  That must mark the falling of a flaming bomb, dropped from one of the big planes in order to get a lead on their location.  Jack believed he had even glimpsed the bridge itself in that brief interval.  How the prospect thrilled him!

Tom, on his part, had little opportunity to observe anything that was taking place earthward.  His duty lay closer at hand, for he knew that a swarm of fighting Gothas had started up to engage the attacking squadron, and realized that one or more of these hostile aircraft might suddenly appear close at hand, bent on bringing about their destruction.