“And I’d be glad to help pull the rope!” snapped Jack.  “A more cowardly act couldn’t be imagined than this.  Air pilots take great enough chances, without being betrayed by spies or traitors.”

“We’d better say nothing about it,” Tom concluded.  “I’m going to run over the entire machine on my own account.”

“And I’ll do the same, Tom; for a pilot can’t be too sure of his mount, especially when there’s such meanness afoot.”

They accordingly busied themselves after their individual fashion.  Every brace and stay was looked over carefully and tested as only pilots know how.  Long experience, and many accidents have taught them where the weak spots lie, and they understand how to guard against the giving way at these points.

So the minutes passed.  Other pilots had already ascended to await the assembling of the picked squadron at some given altitude.  Every minute or two could be heard the rush of some unit starting forth.  There were few of the accompaniments of an ordinary ascent, for all loud cries had been banned.

“All ready!” came the welcome words at last.

The last strut had been carefully gone over, and now everything was pronounced in perfect condition.  At the same time, after such a discovery had been made, it was only natural for the boys to feel a queer tug in the region of their hearts as they climbed to their seats, and with hands that quivered a little proceeded to make fast the safety belts.

“There goes another bomber, which makes four—­the full number you spoke of, Tom,” remarked Jack.  “I suppose we’re holding up the procession more or less, worse luck, when usually we can be found in the lead.”

“The commander must know about our mishap,” replied Tom, “and isn’t apt to blame us for any little delay.  The night’s still young, and we can reach our destination in half an hour, with time to spare.  So cheer up, old comrade; everything’s lovely and the goose hangs high.  Now we’re off!”

With that he gave the word, and paid attention to his motor, which started a merry hum.  The propellers commenced to spin, and down the slight slope they ran with constantly increasing speed.  All around them could be heard the refrain of planes in action; from above came similar sounds, and Jack, looking up, discovered dim scurrying forms of mysterious shape that flitted across the star-decked sky like giant bats.

Now they, too, were rising swiftly in spirals.  Both kept a keen watch, for it was at this time they stood the greatest chance of taking part in an unfortunate collision that might result in a fatal disaster.

But every pilot was on edge, and careful to avoid any such blunder.  They had been well drilled in all the maneuvers connected with just such a hurried ascent in numbers.  Each plane had its regular orbit of action, and must not overstep the bounds on penalty of the commander’s displeasure.

After mounting to the arranged height, the Air Service Boys found that it was a very animated region, though fully a thousand feet from the earth’s surface.  Almost a dozen planes in all were moving in a great circle, their motors lazily droning, and the pilots ready to enter into squadron formation on signal.