"Right, sir," the technical sergeant answered, and grinned as though he could name two or three high rankers he would just love to toss out on their ears, now that he had the permission to do so.

However, he didn't mention that little item. Instead, he snapped orders to the two mechanics, and all three of them began rolling the attack bomber out onto the hangar apron. Meanwhile Colonel Welsh led Dawson and Farmer into Captain Billings' office in a rear corner of the hangar. He snapped on the light, closed the door, waved them to a couple of chairs, and sat down at a desk. He drew six envelopes from an inside pocket of his tunic. Each envelope was heavily sealed with wax, and each was made of a peculiar-looking paper. At first glance it struck Dawson that it was oil paper, or shark's skin. At any rate, he had a sudden thought that each envelope was absolutely waterproof.

The colonel placed them in a pile on the desk in front of him, and then rested a hand on top of the pile, almost as though he expected a non-existent wind or an invisible force to snatch them away.

"You two are headed for Natal, Brazil," he began, speaking quietly. "With stops on the way at Miami, Puerto Rico, San Fernando in British Trinidad, Paramaribo in Dutch Guiana, Belem in Brazil, and Natal. You will land on the government airport at each of those points. Officially, you are making a survey flight for the Army Air Transport Command. At Miami and Puerto Rico you will contact the American commanding officer, and deliver to him in the presence of no one else the envelope that bears his name. On the authority of a letter which I shall give you to take along, you are to instruct him to guard his envelope with his life, and not to open it until the sixteenth of this month. At San Fernando, Paramaribo, Belem, and Natal, of course you will contact the officer in command of the American staff, and not the commanding officer of the airport."

The colonel paused for a moment as though permitting time for his instructions to sink in. Then he tapped the pile of heavily sealed, waterproof envelopes with his fingers.

"These contain information on perhaps the most important secret of this war!" he continued, speaking in a grave tone. "The Axis would gladly give up half a dozen divisions of troops for the possession of any one of these envelopes. And that doesn't even begin to describe how important they are. I am the only man in the world who knows of the flight you two are to begin in a few minutes. At least, I pray to God that I'm the only one. However, in view of the fact that absolutely nothing is sure in this war, I must give you this order: Under no circumstances, not even under the threat of the most horrible kind of death, is either of you to permit a single one of these letters to get into the hands of anybody but the American officer whose name is typed on the front of each envelope. Do I make myself clear?"

"Yes, sir," Dawson said with a nod.

"Definitely, sir," Freddy Farmer echoed.

"And I'm sure you do," the colonel said. "I can't help, though, but stress that point. Don't let any of these envelopes out of your sight until each has been delivered to the proper person. Make doubly sure that each of those proper persons understands what he is to do. Naturally, you'll be asked questions by those officers as to what the envelopes contain. That is one reason why I'm not even telling you, so that you can truthfully reply that you do not know. Just remember, this is the most secret mission you have ever undertaken. Guard these envelopes with your lives and see that they are delivered to the proper parties. If the commanding officer does not happen to be there when you arrive, do not give the envelope to the next in command. Stay there until the commanding officer does arrive. If you have a forced landing, play up the fact you are on a survey flight. If your plane is damaged, a wire sent to me in Washington will get an immediate reply ordering the commandant of the airfield nearest the scene of your crash to turn over a plane to you. If one of you happens to be injured in the crash, the other will carry on alone as soon as possible, without creating suspicion that the flight is not for survey purposes."

The colonel suddenly stopped talking and drew from his pocket two small vials containing a brownish liquid. He placed them beside the pile of envelopes, and looked at the two air aces again.