Hal and Noll tried to keep their own faces expressionless.

Hal Overton never forgot his feelings when he shouldered his rifle, with
bayonet fixed, and patrolled his first sentry post for two hours.

He felt even more the sense of responsibility when he came to his first
night tour of sentry duty.

In his way the sentry is a tremendously important personage. On his post
he represents the whole sovereignty of the United States of America. The
youngest sentry in the Army may halt and detain any officer, no matter
of how exalted rank, until he is certain that the man halted is an
officer entitled to pass. Of course, with a sentry of common sense the
mere appearance of the uniform is enough under ordinary circumstances.
But no personage in the United States may attempt to go by a sentry
without the sentry's permission.

"How'd you enjoy it, Overton?" asked Sergeant Brimmer, who was sergeant
of the guard, when Hal came in from his tour of night duty.

"I hope I didn't get myself into trouble," Hal answered.

"How so, lad?"

"I halted the commanding officer of the post."

"Was he in uniform?"

"No; in civilian dress. He had been to the city, I guess, and was coming
up from the shore. It was dark, and I saw only the civilian clothes. So
I challenged him."

"What did the K. O. say?"

"K. O." is the Army abbreviation for "commanding officer."

"He asked me what I was trying to do?" smiled Hal. "So I repeated my
question, 'who's there,' Then he answered, 'the commanding officer.' I
replied: 'Advance, commanding officer, to be recognized.' He seemed
uncertain about it, but I made him step right up to me. When I saw who
it was I told him to proceed."

"Did you hold your gun at port all the time?" inquired Sergeant Brimmer.

"Yes; until I recognized the commanding officer. Then I came to present
arms, and he returned my salute, then walked by."

"Your skirts are clear enough, then," nodded the sergeant of the guard.

"But why did he ask me, so crossly, what I was trying to do?" asked Hal.

"Why," mused the sergeant, "my own idea of it is that K. O. was trying
you out on purpose. And I'll wager the K. O. was glad to find a rook
sentry so thoroughly alive to his job. Though I doubt if you'll get
commended in orders for just being awake. But that reminds me of
something that happened to me, in the Philippines," laughed Brimmer. "I
was sergeant of the guard out there, and one night the colonel of
another regiment tr