There were only a few high cirrus clouds in the sky late on the morning of March 3 when a pilot took off from Luke in an F-84 jet to log some time. He had been flying F-51's in Korea and had recently started to check out in the jets. He took off, cleared the traffic pattern, and started climbing toward Blythe Radio, about 130 miles west of Luke. He'd climbed for several minutes and had just picked up the coded letters BLH that identified Blythe Radio when he looked up through the corner glass in the front part of his canopy--high at about two o'clock he saw what he thought was an airplane angling across his course from left to right leaving a long, thin vapor trail. He glanced down at his altimeter and saw that he was at 23,000 feet. The object that was leaving the vapor trail must really be high, he remembered thinking, because he couldn't see any airplane at the head of it. He altered his course a few degrees to the right so that he could follow the trail and increased his rate of climb. Before long he could tell that he was gaining on the object, or whatever was leaving the vapor trail, because he was under the central part of it. But he still couldn't see any object. This was odd, he thought, because vapor trails don't just happen; something has to leave them. His altimeter had ticked off another 12,000 feet and he was now at 35,000. He kept on climbing, but soon the '84 began to mush; it was as high as it would go. The pilot dropped down 1,000 feet and continued on--now he was below the front of the trail, but still no airplane. This bothered him too. Nothing that we have flies over 55,000 feet except a few experimental airplanes like the D-558 or those of the "X" series, and they don't stray far from Edwards AFB in California. He couldn't be more than 15,000 feet from the front of the trail, and you can recognize any kind of an airplane 15,000 feet away in the clear air of the substratosphere. He looked and he looked and he looked. He rocked the F-84 back and forth thinking maybe he had a flaw in the plexiglass of the canopy that was blinking out the airplane, but still no airplane. Whatever it was, it was darn high or darn small. It was moving about 300 miles an hour because he had to pull off power and "S" to stay under it. He was beginning to get low on fuel about this time so he hauled up the nose of the jet, took about 30 feet of gun camera film, and started down. When he landed and told his story, the film was quickly processed and rushed to the projection room. It showed a weird, thin, forked vapor trail--but no airplane.