My advice is that we lay flat on the ground, hold our ears and bury our
faces. Immediately after the blast we'll run the machine out and get up
as swiftly as possible."

"I can imagine the effect of the explosion," said Chester.

"Well, I can't," returned Hal; "nor can you. How many men it may kill,
how many it may maim and what damage it will do cannot be estimated. But
one thing sure, immediately afterwards every sleepy German soldier within
fifty miles will be on the alert. The Germans will know it was not an
accident. They will attribute the explosion to a bomb dropped from the
air. We may have trouble reaching our lines."

"I wish you hadn't done it, Hal," mumbled Stubbs, whom the lads had
found hiding beside the aeroplane. "It will dig a hole a mile deep in
the ground. Rocks, guns and everything will come down like hail. We may
be killed."

"Quiet, Stubbs!" ordered Hal. "Flat on the ground with you now. Hold your
ears and bury your faces until I tell you to get up."

He suited the action to the word. Chester and Stubbs followed his
example.

For long moments, it seemed to them, they waited for the sound of the
blast that would shake the country. Each was anxious, for there was no
telling what the result of the explosion might be. Stubbs squirmed
uneasily as he burrowed in the ground, while Chester and Hal were by no
means easy in their minds.

So long did they wait that it seemed to Chester something must have gone
wrong. Perhaps the fuse had gone out. Perhaps another German guard had
discovered it in time and pinched out the fire. There were many
possibilities, and the lad considered them all as he lay prostrate on
the ground.

He was about to raise his head and ask Hal a question, when, suddenly,
the blast came.

There was, at first, a long grumbling roar, which, it seemed, would never
end. Gradually the roar increased until it reached such proportions as to
be beyond all description; it was a roar the like of which neither of the
three figures who lay there had ever heard before--probably never would
hear again.

Louder and louder it grew and then ended in a final blast that was louder
than many thousand times the loudest peal of thunder--louder than the
simultaneous firing of thousands of guns.

Then it became suddenly quiet--so quiet that Hal, Chester and Stubbs, who
had now leaped to their feet, felt a queer sensation hovering all about
them; so quiet that it was, for the moment, impossible to