The U. S. Army Air Transport Command at San Fernando comprised the entire south side of the Trinidad air base. Dawson spotted the American flag atop the Administration Building from the air. After his recent experience, a great sense of relief and joy flooded through him at the sight of Old Glory waving proudly in the breeze. And not only that, but the sight of Old Glory meant also that this crazy aerial messenger-boy mission was one-half completed. Three more stops and they would be at Natal. There they would meet Colonel Welsh and, please, please, God, find out what in thunder this secret sealed-envelope business was all about.

"And if he doesn't tell me," Dawson muttered as he let down the Vultee's wheels and nosed the craft earthward, "it's going to be the end of a beautiful friendship as far as I'm concerned. Right! He's got to give us a tiny inkling, at least or—or—Well, I sure hope he does, anyway."

"So do I, old chap!" he heard Freddy Farmer echo his hope. "I also want to see his face when we tell him what we have to tell. You haven't any new ideas, have you, Dave?"

"Dawson shook his head. During the remainder of the flight to this next stop, both had taken the U-boat experience apart and had carefully examined it piece by piece. It was all to no avail, in regard to reaching any definite conclusion. True, the logical conclusion was that the life raft had served as a decoy to bring them down so low that its occupants could shoot them into the water. When that had failed, the lurking U-boat had surfaced to try its luck with its bow anti-aircraft gun. If that was the correct conclusion, it made everything even more screwy. Colonel Welsh was the only man living who knew why they were making this crazy flight. He had told them so. How could a Nazi U-boat at sea learn the secret they shared with Colonel Welsh? And—

"Gosh!" Dawson gasped. "But no! Heck, no! That would be even screwier!"

"What, Dave?" Freddy asked. "You do have a new idea?"

"Not exactly," Dawson replied. "Just a chilling thought. Do you suppose those birds on that raft were really torpedo survivors, and in their crazed state took us for a Nazi plane and—"

"What utter rot, Dave!" Freddy Farmer interrupted. "Don't be silly, old thing! Of course not! Would four torpedo survivors bother to take four sub-machine guns onto a life raft with them? Certainly not! Come out of it, Dave! They were Nazis, sure enough. They were from that U-boat, too, and set adrift to have a go at us."

"But how—" Dawson began and cut himself off short. "Oh, skip it! If I let myself think any more about the crazy business, I'll forget what I'm doing and crack us up."

"Then for goodness' sakes don't think of it!" Freddy Farmer cried in alarm. "I fancy I've had excitement enough for the rest of this day! So forget things and keep your eye on that field down there."Dawson did just that, and a couple of minutes later he set the Vultee down light as a feather and taxied it over toward the Administration Building. He braked to a stop eventually, unsnapped his safety and parachute harness, and climbed stiff-legged down onto the ground. Freddy Farmer joined him, and they were just starting to get some of the flight stiffness out of their legs when a major came out of the Administration Building and walked over to them.

"Captains Dawson and Farmer?" he asked with a smile.

"Yes, sir." Dave replied with a salute. "I'm Dawson. And you are Major Parker, Yank commandant here, sir?"

"That's right," the senior officer replied. "Welcome to Trinidad. Word came through that you were making a survey flight along our South American bases. I think you'll find we're not doing so badly here at San Fernando. Here, this came through about half an hour ago. It's addressed to you both. Needless to say, we didn't try to decode it. I don't believe we have that code in the base book, anyway."

The major held out a small yellow envelope. Dawson took it, ripped it open, and withdrew a single sheet of paper. His heart did a loop in his chest when he saw that the coded message was signed, "Tiger." That was the signature Colonel Welsh used whenever he contacted the boys in secret. The major had been quite correct, too. The code used by Colonel Welsh was not to be found in the regular base code book, because it was a special one that the colonel had made up himself. This code was not known by more than half a dozen men, two of them being Dawson and Farmer. The value of such a code was that it was so made up that a decoding book, or decoding wheel, was not needed. Once you knew the code, you could read messages from the memory of what the various letters and numbers and symbols meant.

Dave Dawson and Freddy Farmer looked at it together, while Major Parker politely stared off across the base field. The true meaning of the message became instantly apparent to them. Translated in their minds, it read:

Dawson read the coded message three times, absently pulled off his helmet and goggles, ran his fingers through his hair, and glanced sidewise at Freddy Farmer.

"And that is strictly that," he said. "But I wonder what?"

"I don't know," the English-born air ace replied with a shrug of his shoulders. "Frankly, though, I don't think I'm annoyed by this message. Fact is, I'm just a bit glad. Much rather see him tonight, instead of waiting until we get to Natal."

Dawson grinned faintly, and nodded.

"Yeah, I get what you mean," he murmured. "Maybe there's a connection between this and what happened a while ago, eh?"

"If not, I'll be very much surprised," Freddy Farmer said slowly. "And yet I may be a bit balmy to say that. How could there possibly be any connection?"

Dawson shrugged, but made no reply. He stuffed the coded message into his pocket, and turned to where Major Parker was inspecting the Vultee.

"Thanks for giving us the message, sir," he said. Then he added with a grin, "It sort of looks as though we've been fired, you might say. Our superior officer is joining us here at midnight. Would it be all right for us to eat in the Officers' Club and sort of kill time until he gets here?"

"Certainly, Dawson," the major replied at once. "The place is yours. Help yourself to anything you like. So your survey flight is called off, eh?"

"Well, temporarily, anyway," Dave replied. "But don't ask me why, because I wouldn't know, Major."

"Okay, I won't," the other smiled. "I'll ask you this, instead. What kind of trouble did you run into on the way down here?"

"Trouble, Major?" Dawson echoed, and stared at him hard.

"These holes," the senior officer replied, and pointed to a cluster of four bullet holes six inches in from the Vultee's left wing tip. "Somebody been sticking a pencil through the wing skin, eh?"

"No; Nazi slugs," Dawson told him. "We—we came across a surfacing U-boat about eighty miles out. It crash dived right after it sighted us, but it threw up a few slugs in the meantime. We got a couple of its crew, though. We radioed Puerto Rico patrol base and gave them the U-boat's position. Have you heard any report that she was caught and nailed?""None," the major said, and then pointed across the field. "We wouldn't get that sort of thing, anyway. This is a British-owned base, you know. That we're here is a sort of lend-lease in reverse, you might say. And radio stuff such as your call would be picked up by them over there. Too bad, though, you didn't have a couple of depth charges aboard."

"You're telling me, sir?" Dawson echoed with a grim laugh. "I'd have given my right eye for just one! I don't think I hate anything so much as I hate the U-boats."

"You're not alone in that pet hate," the major added. "The U-boat is the one thing we've got to lick, and lick fast, if we hope to win this war. Of course, we are flying a lot of stuff across these days. But it still takes ships to get oil, and gas, and the heavy stuff over where it's needed. Hold everything! Where are my manners? You two could do with a wash-up and something to eat right now, couldn't you?"

"Oh, quite, sir," Freddy Farmer said eagerly.

And for once Dawson had to agree with the perpetually hungry English youth that a little food wouldn't be a bad idea at all. And so, after a quick check of the Vultee to make sure that no stray bullets had damaged anything seriously, they walked over to the Officers' Club with Major Parker. The commanding officer introduced them to a couple of Air Transport Command pilots and then took them into the mess, where a good meal was waiting for them. Major Parker had a cup of coffee while they ate, and conversation was at a dead end for a bit.

Finally, Dawson refused a second cup of coffee and sighed in contentment.

"I guess I was rather starved, sir," he said to the major with a guilty laugh. "Must be that Caribbean air."

"Or the excitement," the major remarked quietly. "A little excitement always makes me hungry enough to eat a horse. You and Farmer are a couple of lucky fellows, you know."

"How do you mean, sir?" Dawson questioned, and gave him a searching look.

The other smiled faintly and appeared to be very interested in something he could see out of the mess window. Then suddenly he turned his head and fixed his calm blue eyes on them both.

"Tiger hasn't given me anything to do for a couple of months," he said, "except this job here and orders to keep my eyes and ears open for sabotage, and all that sort of stuff. I think a little real action would just about save my life."

Dawson tried hard to control the start that the unexpected words gave him, but he didn't succeed very well.

"Tiger, Major?" he echoed, as a little note of caution sounded deep within him.

Major Parker smiled, and a little bit of red seeped up into his leathery face.

"I couldn't help but see the signature, Dawson," he said. "But you have my word of honor that I didn't read it. Because I saw that it was addressed to you two. Colonel Welsh taught me that secret code of his just before he sent me down to this place. I haven't been lucky enough, yet, to have had the chance to use it."

Since their messenger-boy mission had been washed out, at least until Colonel Welsh's arrival at midnight, there was no reason to check Major Parker's connection with Intelligence, but Dave somehow couldn't pass it by.

"I see, sir," he said quietly. "Well, Farmer and I were taught something, too, before we left. We were taught to take an interest in copper discs. Are you interested in copper discs, sir?"

"Slightly," the other said with a chuckle. "At least I'm interested in one copper disc. It has numbers on it."

"Numbers?" Dawson murmured, and tried to look a little surprised.

Major Parker smiled, and slipped a hand into his pocket.

"That's right," he said as he withdrew his hand. "Numbers. The numbers on the copper disc I'm interested in add up to forty-three. Would you like to see it?"

A cold chill shot through Dawson's chest, and a strange dryness came into his throat. Forty-three? But if Major Parker really was Colonel Welsh's agent down here at San Fernando, the numbers on his copper disc should add up to forty-one.

"Why, yes, yes," he finally got out with an effort. "I'd like to see it very much."

"Then have a look, by all means, Dawson," the major said, and with a slight movement of his hand he tossed a brightly polished copper disc down on the table top.

Dawson picked it up with fingers that were trying desperately hard to stop trembling. He could hear Freddy Farmer's heavy breathing, as the English youth leaned over to take a look. Dave had picked up the disc with the smooth side showing, so he had to turn it over. On the other side stamped into the metal were the numbers 9 1 2 7 8 6 8. He stared at them, and suddenly the truth came to him. The numbers did not add up to forty-three. They added up to forty-one, just as they should have.

The major's soft chuckle made Dawson jerk up his head.

"Sorry I couldn't resist the temptation, Dawson," the officer said. "You just added them up, didn't you? And reached the Pearl Harbor figure, eh?"

"Yes," Dawson said, and handed back the copper disc with a grin. "But you sure had my heart fluttering for a moment there."

"Frankly, I was just about to reach for my service automatic," Freddy Farmer added.

"Well, forgive me my rather flat little joke, and let's skip it, eh?" Major Parker said with a little wave of his hand. "I noticed that Tiger stuff gave you a little start, so I thought I'd kid a bit. Maybe that's what this darn sun down here does to a fellow. To be serious though—and out of order, I guess—anything in Tiger's message that I should know?"

"Just what we told you," Dave replied pleasantly. "Our survey job is held up until Colonel Welsh arrives. Which will be midnight tonight."

Major Parker looked disappointed. Then he sighed, and grinned.

"Okay," he said, "we'll let it go at that. If he had wanted me to know anything, he'd have sent me a message, too. Well, as I said, the place is yours. I've got some paper work to do, so I'll have to leave you for a spell. Don't hesitate to make yourselves at home. If there is anything you want, just yell. See you later."

"Yes, sir, and thanks for everything," Dawson said. He and Farmer also rose as the senior officer got to his feet.

"Think nothing of it," the major said with a wave of his hand. "And have fun, if you can find any fun around this place." With a smile and a nod, he went through the mess door.

Freddy looked at Dawson, and Dawson looked right back at him.

"Nice enough chap, isn't he?" the English youth finally broke the silence.

"Yes, he's okay," Dawson agreed. "I guess he is going bats down here with nothing to do. That is, nothing in his own line of work. Say, Freddy?"

"Yes, Dave."

"How about walking down some of this swell meal, huh?" Dave suggested. "I could do with a walk around. And like Colonel Welsh, I'm not so keen about four walls."

"A top-hole idea," Freddy Farmer said gravely, and brushed a couple of crumbs off the skirt of his tunic. "I know just what you mean, old thing. I've been thinking about it myself. Yes, definitely a top-hole idea. Let's get along, shall we?"

"Yeah, let's," Dawson murmured, and led the way toward the mess door.