I've flown P-38 exclusively in various games and simulators for about five years, and I've never once executed a proper hammerhead in combat. Instead, I do a sort of hammerhead on the pitch axis instead of the yaw axis, simply pulling back on the stick instead of giving hard rudder in one direction. It's more effective and a lot easier to do. It's best to do this at the top of a hard climb, but you shouldn't be doing that at all in the P-38 unless you've got a great energy advantage over your opponent. The P-38 climbs best at a shallow angle, no more than thirty degrees. Again, only do a steep climb if you've got an extra couple of hundred miles per hour or a few thousand feet over your opponent. And that's when my sort of hammerhead comes in handy.