The North American P-51 Mustang
All WWII aviators flew the trainers. Most of the trainers were easier to fly the further up the chain the recruits went. When they graduated, that would assure a qualified cadet. Now the hard part, flying in war. The Ryan, Stearman, Vultee "Vibrator" and T-6 Texan were everywhere around the U.S. during the war, training thousands of pilots. Many WWII trainers still exist and fly regularly.