etachment was under way. In about an
hour the position ordered had been taken.

"Here comes the first Navy birdman!" cried Dan suddenly, pointing
townward.

Just appearing over the housetops, and soaring to an elevation
of a thousand feet, came one of the huge hydro-aeroplanes in which
Navy aviators had long been practicing for just such work as this.
Capable of coming down and resting on the water, or of rising
from the same, these aircraft were ideally suited to the work.
Swiftly over Vera Cruz came the airship, then straight out over
the advanced line, and next on toward the detachment beyond.

"He isn't coming down," cried Danny Grin in a tone of genuine
disappointment. "No chance for you on that one, Davy! Too bad!"

Yet suddenly the rattling noise nearly overhead almost ceased
as the engine was shut off. Then gracefully the craft voloplaned
and touched the ground, just inside the detachment's line.

"Great work, Bowers!" cried Trent, recognizing in the Navy birdman
a former classmate at Annapolis.

"Thank you, Trent. You have an officer, haven't you, to help
me with field notes on this survey?"

"I have two," smiled Trent, "but I am afraid I can spare only
one. Lieutenant Bowers, Ensign Darrin. Hop aboard, Darrin!"

In a twinkling Ensign Dave had shaken hands with the birdman,
adding:

"At your orders, sir!"

Then Dave stepped nimbly up to the platform. "Take a seat beside
me, with your field-glasses ready. Here's your field note-book."

At a sign from Lieutenant Bowers, the eager sailormen parted in
front of the airship, which, after a brief run, soared gracefully
once more.

Behind Lieutenant Bowers stood a sailor with a signal flag.

"Step to the rear," Bowers directed, over his shoulder, "and wigwag
back: 'O.K. Stopped only for assistant.' Sign, 'Bowers.'

"Aye, aye, sir," answered the signalman. "Lieutenant Sherman's
airship is rising from the harbor, sir," reported the signalman.

"Very good," nodded Lieutenant Bowers, and kept his eyes on his
course. "Darrin, are you taking all the observations necessary and
entering them?"

"Aye, aye, sir."

"There's the railroad bridge about which the admiral was so anxious,"
said Bowers, presently. "You will note that the bridge stands, but
the railroad tracks have been torn up."

"Aye, aye, sir," Dave reported, after using his field glass.

"That's one of the things we wanted to know," Bowers continued.
"And keep an especially sharp