MARSHALL HEADLE, Lockheed’s chief test pilot, was getting himself supercharged. For half an hour he had exercised on the bicycle apparatus while breathing in pure oxygen through his face mask. Now the nitrogen content of his bloodstream had been lowered to a safe level and he was ready to test one of the world’s fastest airplanes. Lockheed’s new P-38 interceptor pursuit can climb to thin air so fast that an unprepared pilot would get the bends, the same malady that affects deep-sea divers who rise from the depths too rapidly. To prevent bubbles of nitrogen from forming in his blood the pilot has to supercharge himself with oxygen before he leaves the ground. Testing airplanes at speeds that are faster than anyone ever flew before introduces some strange problems. Several of the newest American fighting planes are so fast that it would be too dangerous to test them at their all-out top speeds. Engineers know that the terminal velocities of some of these planes are around 700 miles per hour. From a 30,000-foot altitude such a plane would hurtle in a dive to sea level in twenty or thirty seconds. The pilot wouldn’t have time to pull out of his dive after reaching terminal velocity. Even coming downhill at 500 miles per hour puts a strain on the pilot. Passengers on transports that descend 500 feet a minute are fairly comfortable but a test pilot may come down a hundred times faster. The descent into dense air is so rapid that he would suffer from sinus pains and might even cave in his ear drums if he didn’t remember to shout all the way down to help equalize the pressure. You could count almost on the fingers of one hand the number of pilots who have flown faster than 450 miles per hour in level flight. Flying an airplane at 500 miles per hour is very much the same and at the same time is very different from flying a slower airplane. To Headle, 500 miles per hour feels the same as 150 miles per hour as long as he holds the plane in straight and level flight. But it’s different when he lets the plane deviate from its straight path. Pilots have passed out when pulling out of a terminal velocity dive too rapidly, and in a 500-mile-per-hour plane the same thing can happen merely by banking the plane into a turn. Headle has to take his turns gradually or else slow down for them. If that's the case, what good is excessive speed in a military airplane? The advantage is that a high-speed interceptor can save precious minutes getting off the ground and up to the scene of a fight, after which the pilot can throttle down to a safe maneuvering speed. Pilots are least affected by changes of acceleration when they are lying down, and in the future it may be that cockpits will be built so that the pilot lies on his stomach, facing forward, to help keep him conscious while maneuvering at high speed. Too, by practice a pilot can increase his resistance to fast changes of direction. If Headle had room for passengers in the P-38 he could keep them unconscious as long as he pleased simply by making turn after turn that were sharp enough to affect them without being so sharp as to affect himself. At high-flying speeds gunnery becomes something quite different from what we are accustomed to. At wide-open throttle some modern planes can fly faster than a heavy revolver bullet. A gun fired broadside at another plane on a parallel course must be pointed considerably ahead of the target because wind resistance will give the bullets a curved path. These days a pilot could even fly into bullets that he fires from his own gun if he points the gun up at a slight angle to give the bullets a trajectory that will bring them down into his flight path at the same instant that his plane reaches that point. Airplanes in the 500-mile-per-hour class not only were an impossibility a few years ago but it was then generally assumed that speeds much in excess of that figure never could be attained. The text book supposition has been that the highest possible airplane speed is represented by the speed of sound minus drag. This is based on the fact that at the speed of sound, which is 750 miles per hour, compressed air begins to pile up in front of the wing, creating tremendous resistance. Other factors reduce  this highest probable speed down to around 600 miles per hour. But Hall L. Hibbard, chief engineer of the Lockheed Aircraft Corporation, like a number of other leading designers, has a different idea about top speeds. “The trouble with the speed-of-sound theory,” Hibbard says, “is that airplanes have already moved faster than the text books say they can, Planes have been dived at 625 miles per hour. In several cases where speed governors broke, propeller tips have moved faster than 750 miles per hour. The fact is that the speed of sound is no barrier at all but simply an obstacle that must be overcome before planes can fly faster. “One estimate is that 2,000 horsepower per ton of weight would be needed to move an airplane 750 miles per hour. Our best engines today weigh in the neighborhood of one pound per horsepower, so while an engine might conceivably fly itself that fast it could not have any airplane or pilot attached. “More power out of lighter engines would be one way to beat the problem, but some more efficient answer probably will be found. For instance, is there any way by which we can prevent the compression wave from forming in front of the wing?” Lockheed has just finished a $150,000 wind tunnel in which air speeds up to 260 miles per hour will be developed and in which high-speed problems are going to be attacked. One program will hunt the answer to boundary layer control, control of the thin layer of air that touches the sur- faces of a wing and that seems to get “sticky” at high speeds. Boundary layer studies possibly may point the way to eliminating or dissipating the compression wave in front of the wing, and permit higher speeds. Opposite-turning propeller blades on the same shaft, being studied at Stanford University, is another improvement that may help airplanes fly faster. The P-38, the fastest thing yet to come out of Lockheed’s speed department, is a fantastic airplane. First, because it is an ungainly monster that resembles no other | airplane on earth. Second, because it has the easy handling characteristics of a normal airplane in spite of its terrific speed. Record-smashing planes of the past were stressed right up to the breaking point, they were stripped down to bare essentials, their hopped-up engines had to be replaced after every run, and they carried limited fuel. Every landing was a separate adventure. On the other hand, the P-38 lands easily and safely. Its fuel capacity gives it an extended range, its engines require only normal servicing, and it carries the usual armament, radio, and other facilities in addition to its pilot. Fast as it is, it is a sturdy and reliable plane. The plane’s wing resembles that of a bimotored transport and its two opposite-turning Allison in-line engines develop approximately 2,000 horsepower. The pilot sits amidships over the wing. The double tail group is attached to the wing by two booms. Weighing more than six tons and having a wing span of fifty-two feet, it is a lot of airplane for the single pilot on board. Lockheed’s speed department has experimented with all sorts of designs in its quest for more speed. Flying wings have been studied and tail-first airplanes that appear to be flying backward have been considered. No one knew what the P-38 would look like before it was designed and today no one can say what a 1,000-mile-per-hour airplane is going to look like. “Eight hundred and 1,000-mile-per-hour airplanes aren't in sight yet but they are on their way,” Hibbard declares. “The problems that such speeds present are difficult but are not as difficult by comparison as the problems that man had to solve before he could fly at all. Now that we know how to fly much of the work of designing and building a plane that will pace the sun has already been done.”