Two Republic P-47 fighters are reported to have attained diving speeds of 725 mph. while piloted by AAF Lts Harold Comstock and Roger Dyar. Both dives were made from the 35,000-ft level. Lt Comstock states that in his super-hurtle he was unable to move his elevators, so stiff was the flow of air, though Lt Dyar found that he had some control. But both pilots felt obliged to crank their trim tabs in order to pull out. Comstock experienced a shuddering in his plane which the company interpreted as a possible approach to the critical speed (736 mph, the speed of sound at sea level) at which an airfoil presumably loses its various flight characteristics.