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.

CHAPTER VII

THE BATTLE IN THE AIR

The din soon became general, one after another of the American planes joining in the battle.  The German aircraft held off a little, fighting from afar, evidently thinking to accomplish their ends without taking too much risk.  Had they boldly assaulted, doubtless the result would have been much more disastrous to both sides.

The big bombers had but one object in view, which was to bomb the important target below.  To drop an explosive on a certain spot had been the most important training of those aboard these craft.  They had been carefully selected from the ranks of the many observers taking service in the aviation branch of the service; and great things were expected of them now.

The Huns had concentrated the glare of numerous searchlights on the hub of the squadron’s activities, so that the speeding planes could be seen darting hither and thither like bats during an August evening, darting around some arc-light in the street.

The flash of the distant guns aboard the planes looked like faint fire-flies in action.  No longer was the earth wrapped in darkness, for flares dropped by the bombers kept continually on fire.  The bridge stood plainly out, and a keen eye, even without the aid of glasses, could distinguish the rush of terrorized German troopers trying to get clear of the danger zone before a well directed bomb struck home.

Jack, leaning from his seat, took all this in.  He was keyed to the top-notch by what he saw and heard.  Tame indeed did most other incidents of the past appear when compared with this most stupendous event.

“Wow!” burst from his lips, as a sudden brilliant flash below told that the first huge bomb had struck; but with all that racket going on around of course no ordinary human voice could have been heard.

He could see that it had not been a successful attempt, for the bomb struck the ground at some little distance away from the terminus of the structure spanning the river.  However, it did considerable damage where it fell, and created no end of alarm among those who were near by.