With a m.u.f.fled exclamation of surprise the man jerked himself forward and Joe went hurtling over his head, his arms, however, still clasped tightly about the other man's neck.

Joe knew in an instant that he was in combat with a man larger and more powerful than himself, but his own youth and suppleness were in his favor.

Throwing all his strength into the movement, he twisted about and at the same time jumped, so that he managed to wrap his legs about the other man's waist. With another lithe movement he was again upon his back and reaching for his antagonist's throat, at the same time squeezing with all the strength of his powerful young limbs upon the other's ribs.

Back and forth across the narrow confines of the little room they staggered, now one having a temporary advantage, and again the other.

Just as Joe was managing to fasten his fingers in at the throat, and the other was hammering terrible elbow blows into his stomach, the bigger man stumbled. As he fell he turned, and his full weight came down upon the lad, almost crushing him.

Joe was not done for yet, however. With the strength of desperation he held on to the other fellow's shirt. He felt something hard and metallic under it, and in a new grasp included that in his fist.

Again the struggle began. Unable to break Joe's grip, the intruder tried to sink his teeth into the lad's wrist. Failing in this, he gave an evidence of his strength by rising, dragging Joe upward with him.

There was an instant of terrible whirling about the room, and then the man landed a smashing blow on Joe's jaw. Still gripping the man's shirt, and the unknown metallic thing beneath it, the lad reeled. The shirt ripped, there was another sharp snap, and the boy fell backward, dazed.

He heard the man run swiftly, almost noiselessly toward the stern of the ship; brilliant and many-colored lights flashed before his eyes--and he knew no more.

[Ill.u.s.tration: There was an Instant of Terrible Whirling about the Room.]

CHAPTER VI

THE MYSTERY OF THE IRON CROSS

When Joe came back to consciousness it was with his head pounding terribly, and Lieutenant Mackinson bending over him, swathing his face with a cool wet cloth, while Jerry and Slim, whom the lieutenant had wakened, were standing nearby, one holding a basin of water, the other a bottle containing a liniment or lotion.

"You've been done up pretty badly," said Lieutenant Mackinson, as Joe went through the painful motion of moving his head from left to right, letting his gaze take in the now lighted wireless room.

"Yes," he answered with an effort. "Nothing serious, though, I guess."

And then, full recollection coming to him, "Did he get away?"

"Who?" asked the lieutenant quickly. "Who was it beat you up so?"

"I don't know," Joe answered. "I discovered him in the battery room. We fought in the dark."

With the aid of the others he raised himself to a sitting posture, then stood up and walked rather unsteadily across the room, took a long quaff of cold water and dropped heavily into Lieutenant Mackinson's Morris chair.

At the same time he gazed for the first time at what he had been holding tightly clutched in his right hand ever since the knockout blow had been delivered. The other three also were staring at it in open amazement.

"What is it?" asked Joe, as the lieutenant crossed the room and took the thing from him for a closer examination.

"What is it?" Lieutenant Mackinson repeated. "Why, lad, this is the German iron cross! Tell us what happened here."

With the young officer seated before him, and his two pals standing at either side of his chair, Joe, quietly, quickly and as carefully as he could, gave them every detail of the occurrence, from the moment he had first heard sounds in the battery room, to the time that the other man ran away and he lapsed into unconsciousness.

While Joe was relating his story the lieutenant examined and re-examined the iron cross, the bit of broken chain still attached to it, and the piece of brown woolen army shirt which the lad had torn away with it.

As the latter finished, the young officer hurried into the battery room, accompanied by Slim, to make a survey there.

In ten minutes he returned, his face pale, his jaws clenched.

"There must not be a word of this to anyone," he warned them. "I am going to report to the captain at once. Someone has been tampering with the batteries, and he had with him a portable wireless which he evidently intended to attach."

"You're the original little discoverer, all right," said Slim in open admiration, addressing Joe as the lieutenant hurried from the room. "And you certainly were game, to take the beating you did."

"Yes, he punished me some," Joe admitted. "But I got in a little work on him, too. The only trouble is that I'm afraid I didn't blacken an eye, or break a jaw, or otherwise do any damage that might be apparent and so lead to the fellow's discovery."

"The nerve of it, though!" broke in Jerry.

"A German spy, doubtless masquerading as an American soldier, and right here on a United States transport loaded with fifteen hundred soldiers and tons of guns and ammunition."

"Yes," said Joe contemplatively, "that's the very serious part of it all--the fifteen hundred soldiers and tons of guns and ammunition."

"Sh-h-h-h!"

Slim, who was standing nearest the door, had heard footsteps. A moment later the lieutenant reappeared, accompanied by the captain of the _Everett_.

When the boys had been presented, the captain abruptly requested Joe to repeat every detail he had told Lieutenant Mackinson. As he did so the captain gazed compa.s.sionately upon his injuries.

"And where is the instrument that you discovered?" he asked of the lieutenant when Joe had concluded.

The young officer stepped into the battery room, returning with a small, but evidently powerful, portable wireless transmitter and receiver.

"H'm," exclaimed the captain, examining it carefully. "Of German make."

"Exactly, sir," replied Lieutenant Mackinson, "and evidently quite new--probably never used more than once or twice before."

"This is very serious business," said the captain impressively. And then, addressing Joe: "Did you get a look at the other man? Would you know him if you ever saw him again?"

"No, sir, I did not even get a glimpse of him. But I thought, sir, that perhaps----"

"Yes," encouraged the captain in a kindly tone. "Go on with your suggestion."

"I thought, sir," Joe continued, "that if we could find a man aboard with his shirt torn in such a way that this piece would fit, and especially if he had the other end of this chain in his possession, then it might be pretty definitely a.s.sumed that he was the man who was in the battery room."

"The chain--perhaps," said the captain slowly, "although that seems doubtful. As to the shirt, no."

And, unb.u.t.toning his jacket, he produced from beneath it a torn and crumpled brown woolen shirt.

"We found this about twenty feet from here as we were on our way," he continued. "It resembles, but it is not, a regulation army shirt. It is of the same texture and color, but it differs in minor details easily discernible. It is my opinion that the man who wore this shirt bought it and wore it for this very purpose, so that, if necessary, he might discard it and still have the one which came to him through the Quartermaster's Department. We evidently have to deal with a very crafty enemy, and one as bold as he is unscrupulous.

"Lieutenant, what do you make of his manipulations in the battery room?"

"There is no doubt in my mind, sir," Lieutenant Mackinson answered, "that he was about to connect up this instrument and then hide it for future use where it could not easily be seen."

"I believe you are right," said the captain. "And then what use did he intend to make of it?"