The General Motors P-75 turned out to be a short-lived, long-range escort fighter; the contract for 2,000 of them was cancelled.
P-75A), with its contra-rotating propeller, was a big airplane—too big, in General Bradley's opinion.
Through General Motors, the P-75 project had been launched in late 1942. To get into production quickly, the plan was to use, as far as possible, parts already in production for existing aircraft. The double Allison V-3420 24-cylinder engine and a double rotating propeller were to be the only new features. The wings were to come from the P-40, the center section from the Navy's Vought Corsair FU-9, the tail from Douglas' A-24 bomber. With an initial order of 1,000 planes, General Motors had started production on an emergency basis at its Fisher Body Plant in Cleveland. Anxious to fly the P-75, I lost no time in getting to Cleveland to take it up.
The airplane, with its contra-rotating propeller, was a big one—too big. It was heavy, and worst of all, clumsy and unstable. If it had been able to go the required distance, it never could have defended itself. No fighter pilot would endorse it, I was certain. To me, it was hopeless.
I returned to Wright Field more determined that ever to resume my project of extending the range of the P-51. Given enough time, certain defects of the P-75 could be corrected, I knew, but there was not enough time. As I look back today, I am certain that its weight, excessive size and basic instability would have prevented the P-75 from ever being a successful fighter.
Before going to Cleveland to fly the P-75, I had gone out to the hangar to do a little -simple barnyard research on the P-51 configuration. At that time the P-51 had about 200 gallons of fuel in its wings and we were adding two 75-gallon drop tanks, one under each wing. But to go to Berlin, fight and get back to England safely, it needed more internal fuel. I looked behind the pilot's seat and found only the plane's two radios, the IFF ("identification friend or foe") and the VHF. It was obvious that a tank of considerable gallonage could be put there if the radios were moved to another location but, as you may have guessed, it wouldn't be that simple.
I knew that North American engineers had considered putting a gas tank back of the pilot's seat and had discarded the idea because of fear that a full tank would cause a dangerous shift aft of the center of gravity. The danger was there, I knew only too well, but I had come back from Europe swearing to right a desperate situation and was convinced that it was going to take audacious, if not downright extreme measures. I figured that a full tank of eighty to ninety gallons might well require two hands on the stick for takeoff and climb, and perhaps for a considerable time thereafter. But it seemed logical that after the climb-out and cruise over the North Sea, the weight of the fuel would be sufficiently reduced to assure a return to normal stability. I was just this far along in my thinking when I went to Cleveland to fly the P-75. Upon returning to Wright Field, I went immediately to see General Orval Cook, then head of the Production Division and my immediate boss.
"Orval", I said, "I am just back from flying the P-75 and I cannot believe what I've heard! We've ordered 2,000 of them
The P-51 Over Berlin, by Mark E. Bradley