This air tactic was purely defensive in nature, and could only be mounted by flights of multiple planes working together. The tactic involved all members of the defending formation forming a horizontal circle in the air when attacked. This way, each plane would theoretically protect the plane in front of him. It was thought that an attacking fighter would be unable to attack any member of the formation without coming under fire himself.
The tactic was intended for slower, less capable aircraft when attacked by aggressive enemy fighters. Luffberry Circles were most often utilized by bomber aircraft, although some instances of obsolescent fighters forming Luffberies against more advanced fighter types also occurred, as a way of avoiding dog fights. Bomber formation using Luffberies had the added benefit of defensive gunners that further prevented enemy fighters from attacking the formation.
The tactic appeared very early in the history of military aviation, at the very dawn of air combat, and as such was thought to be flawed and obsolete even by the end of World War I. The Luffberry circle, while generally effective against horizontal attacks by faster aircraft, was very vulnerable to attacks on the vertical plane. For a fighter diving on a target from above, the Luffberry provided perfect targets on a slow, predictable course. As performance and armament of fighter aircraft improved during the First World War, and fighters became capable of high-speed hit-and-run attacks in the vertical, a Luffberry would put the defenders at a gross disadvantage.
By the beginning of World War II the Luffberry was still used by many countries, generally as a last resort measure for poorly trained pilots of less progressive air forces. For instance, this was often used by Japanese kamikaze pilots at the end of the war. The advent of faster allied aircraft resulted in the more maneuverable Zero resorting to the tactic in an attempt to lure their opponents into a turning contest in which they could prevail easily.
Lundstrom in chronicling the operational history of US carrier-based activities in the Pacific from Pearl Harbor through the Battle of Midway provides an extensive discussion of fighter tactics of the time. In the Battle of the Coral Sea, US Grumman F4F Wildcats defending the USS Lexington against Japanese dive bombers adopted a Luffberry Circle when themselves attacked by A6M Zeros.
For any modern aircraft, the Luffberry would seem to be a deathtrap, exposing them to missiles and unchecked gunnery passes. However, US pilots found the North Vietnamese MiG-17 fighters using it as bait for faster F-4 Phantom fighters that did not possess a gun and could not use their missiles due to tight turns made by the MiGs.
Mostly in WWII literature, a Luffberry Circle can be used to refer to any turning engagement between aircraft, i.e. what is more properly known as the Turn Fight or the Knife Fight in air combat tactics. In modern discussions of air-to-air tactics, Luffberry Circle usually refers to a prolonged horizontal engagement between two fighters with neither gaining the advantage.
Raoul Lufbery was the leading fighter ace of the Lafayette Escadrille in WWI, with 17 confirmed victories. Despite the similarities in name, he did not invent the Luffberry circle. It is unknown what, if any, connection the name of the tactic has to this ace.