All three times, I rolled the ship onto its back in a typical Split-S, from altitudes above 35,000 feet - once from above 45,000 feet. I don't remember the actual indicated airspeeds at entry, but am sure they were normal cruising speed for the altitude.

It's hard to say with accuracy what maximum airspeed was attained. To begin with, standard production instruments weren't capable of test-quality recording. But mostly, I was too focused on the ground to give much attention to the instrument panel. In each dive, the needle was jammed on the stop, so it's a good educated guess that maximum speed reached 650 - 670 miles per hour. I know that the tech manual warned against indicated air speed over 400 MPH above 25,000 feet, but we regularly ignored the manual in this and other limitations.

I'm certain of one thing, though. I've heard pilots who claim to have reached Mach 1 in a P-47, but no propeller-driven airplane ever reached Mach 1 - not even the mighty Thunderbolt. It's just not possible, because, at that speed, the propeller no longer delivers thrust, becoming instead a drag which prevents further acceleration.

Here, step-by-step, is the behavior of the airplane in compressibility and our method of dealing with it:

First, we were told not to try using trim tabs for control or recovery. Tabs should be set at neutral because over control would probably result if they were moved and did influence the airplane. Manual pressure was adequate to pull out of the dive, if sufficient altitude was available - high mountains could be a problem, for example.

Upon entering a vertical dive in a P-47, rapid acceleration was inevitable and, at high altitude it was exaggerated. At about 550 MPH indicated, buffeting became evident and it rapidly became severe. The control stick jerked violently in all directions and it was necessary to hold on firmly, with both hands, to manage it. Quite suddenly, the buffeting stopped and the stick became rigid - as though set in concrete. At that point, you jammed both feet hard against the rudder pedals and pulled back on the stick with all your strength - still with both hands. And you stayed that way, simply waiting for the airplane to respond.

In the vicinity of 15,000 feet, depending on atmospheric pressure, the nose of the airplane began to slowly creep toward the horizon. The rate of movement increased as altitude decreased. Level flight could be restored by 8,500 feet if you were willing to absorb the G-force punishment. In my last two dives, I pulled out gradually attaining level flight a bit below 4,000 feet with the airspeed needle still on the stop.

I'm not an engineer so cannot speak with technical competence, but I know of only one other propeller-driven airplane capable of such unrestrained dives - the P-38. And the Lightning had a tendency to "tuck under" early in the dive which made for a greater loss of altitude during the pull-out. It too, experienced buffeting.

I had a good friend who commanded a squadron in the South Pacific. They were equipped with Thunderbolts for most of his tenure. With the arrival of B-29s, their group was assigned escort duty and furnished with P-51s because the longer range of that fighter allowed them to stay with the big bombers all the way to Japan. They lost four pilots before learning that the Mustang couldn't be dived with the same impunity as the Thunderbolt. In each case, the left wing folded up and over the canopy, making escape impossible.

I've been told that compressibility dives killed some Thunderbolt pilots before the recovery procedure was worked out. And I've read that early P-47 models, the ones having fabric-covered control surfaces on the tail, sustained damage to those surfaces. But, by the time the Jug got into combat, it had evolved into a very tough airplane that could absorb a lot more punishment that its pilot could.

Since composing this essay, I've learned that Col. Arlie J. Blood was a member of the team of pilots who developed the procedure for recovering from compressibility dives. Blood later joined the 405th Fighter Group and was my flight leader in the 510th Fighter Squadron until, in 1944, he was shot down by ground fire in Normandy. He escaped and returned to the Squadron. He remained in the service and completed a very distinguished career. Arlie Blood was the most skilled pilot and best leader with whom I ever flew.