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.

Besides, constant vigilance was the price of safety in other particulars. With almost a dozen of their own planes speeding through space, a false move on the part of a careless pilot was apt to bring about a collision that could have only one result.

Jack made a discovery just then that caused him to cry out.

"The signal, Tom! We are to drop down and give the bombers a better chance to get there. No matter what the cost, we've got to reach that bridge to-night!"

Already Tom was changing the course. They had begun to swing lower, each unit of the attacking squadron in its appointed place. A brief interval followed, and then came the bursting shrapnel again around them, while from several quarters close by hovering German planes commenced using their machine guns, to be answered by the challengers in like manner.