"Darrin," decreed Danny Grin.

"How am I to decide?" asked the lieutenant, smiling at the two eager faces. Then, suddenly he added: "I have it! Which excelled the other in map work at Annapolis?"

"Darrin had the higher marks! I defy you to dispute that, David, little giant."

As Danny Grin's statement was true, Dave could not dispute it, so be contented himself by saying:

"Dalzell's map-work at Annapolis was good enough to suit any need around here, and I shall be glad to see Dalzell get the chance."

"On that showing," returned Trent, "Darrin shall have the chance if it comes this way."

After a quick meal the detachment 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 cla.s.smate 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-gla.s.ses 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 a.s.sistant.' 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 gla.s.s.

"That's one of the things we wanted to know," Bowers continued.

"And keep an especially sharp lookout, Ensign, for any signs of Mexican forces, hidden or in the open."

But, though Dare looked constantly, he saw no indications of the Mexican column with which General Maas had retreated.

"Too bad about Cantor of your ship," murmured Lieutenant Bowers, a little later. "Though the forces have been searching for him for three or four days he can't be found anywhere. It must be fearful to be tried for treason to one's flag. I am hoping that Cantor will be brought in dead. Under such charges as he faces, there's more dignity in being dead."

"Much more," Dave a.s.sented, in a low voice.

On and on they flew. Once, when Dave sighted moving persons in the distance, Bowers drove the craft up to three thousand feet above the earth. But soon, under the gla.s.s, these suspects turned out to be a party of wretched refugees, hurrying, ragged, barefooted, starving, gaunt and cactus-torn, to safety within the American lines at Vera Cruz.

For many miles Bowers's craft flew inland, and much valuable information was picked up, besides the data from which any naval draughtsman could construct a very good map of that part of the country.

At last Lieutenant Bowers turned back.

Suddenly Dave exclaimed, "Hullo! There are two men coming out of the adobe house ahead."

The house in question was out about four miles beyond Trent's station.

Dave kept his gla.s.s turned on the two men on the ground, at the same the trying to conceal the gla.s.s from their view.

"They haven't rifles," he told Lieutenant Bowers. Then, as the aircraft pa.s.sed and left the adobe house to the rear, Darrin bent over and whispered something in Bowers's ear that the signalman behind them could not hear.

CHAPTER XXIII

THE DASH FOR THE TRAITOR

A Little later the hydro-aeroplane returned to Lieutenant Trent's position.

Dave placed in the hands of the lieutenant the field note-book, which had been so carefully kept that any officer could draw a map from it at need.

Lightly the big airship touched the earth just inside Trent's line. Dave, shaking hands with his temporary commanding officer, added:

"Thank you for something I've always wanted---a flight over a real enemy's country."

"I've greatly enjoyed having you with me," Lieutenant Bowers responded.

"Trent, you've obliged me hugely by giving me so good an a.s.sistant.

Good-bye, fellows."

The birdman was again several hundred feet up in the air.

"What kind of a trip was it?" asked Dalzell.