on for a great infantry advance. But I understand that this
time they expect to go forward before the end of to-day."

"Which, means," added Lieutenant Mackinson, "that we probably will get a
chance to get right into the thick of it."

On and on they went, and nearer and nearer to the scene of actual battle
they came. They passed the third-line trenches, and now, in places, they
seemed to be in a straight line with some of the concealed artillery
that was pounding away at the enemy in terrible detonations that shook
and rocked the ground every minute.

At the second-line trenches their orders called for a halt. They did not
have to be told that there was "something doing." The road, so far as
the eye could reach backward over the route they had traveled, was a
constantly moving line of motor trucks, coming forward with men and
shells, while out ahead of them, tremendous and menacing, big tanks--the
biggest things the boys ever had seen propelled on wheels or
tractors--were pursuing their uneven course toward the front, in
preparation for a new kind of assault.

"They look like miniature battleships on land, don't they?" exclaimed
Slim.

The others agreed that it was about the best description that could be
given of these massive fighting machines, equipped with guns and men,
that could travel with their own power practically anywhere, across
shell holes, over trenches, through barbed wire--the most human piece of
war mechanism that had yet made its appearance on the battlefield.

Summons to a long-delayed meal gave a welcome interruption to their
guesses as to just what their first duties would be, and they had
scarcely finished their substantial rations of food when an orderly
informed Lieutenant Mackinson that he was to report at once to the field
headquarters.

"Await me here," he said to the five men under his immediate command. "I
probably will be only a short time."

And, indeed, it seemed to them that he had hardly time to reach the
headquarters when he was seen returning hurriedly. He gave some hasty
instructions to the chauffeur, and the latter immediately began a quick
examination of his engine and tires, which promised another early move.

"We go forward as far as we can by automobile again," the lieutenant
informed them, "and after dark to-night we are to establish an outlying
communication from the farthest skirmish points to headquarters."

Almost as he finished the sentence, they were started,