Named for German World War I ace Max Immelmann, the Immelmann Turn is an aerial maneuver in which an aircraft accelerates and executes an ascending half loop. At the top of the loop, when the aircraft is inverted, the pilot executes a half roll to achieve level flight in the opposite direction at a higher altitude. With the advent of high-performance fighters, this maneuver has become less effective.
The modern Immelmann Turn is somewhat different from Immelmann's original combat maneuver which saw the attacker dive on an opponent then zoom climb back to a higher altitude. At the top of the climb, with the aircraft nearing stall speed, the pilot would apply full rudder to spin the aircraft around to make another attack run. This tactic began to fall into disuse late in World War I as fighter pilots realized they were extremely vulnerable at the top of the climb.
The opposite maneuver to the Immelmann Turn is the Split-S.