by simple two-dimensional turns, such as during a car chase. BFM not only relies on an aircraft's turn performance, but also on the pilot's ability to make trade-offs between airspeed (kinetic energy) and altitude (potential energy) to maintain an energy level that will allow the fighter to continue maneuvering efficiently. BFM also relies on the pilot's understanding of the geometry of pursuit within the three-dimensional arena, where different angles of approach can cause different rates of closure. The fighter pilot uses these angles not only to get within a range where weapons can be used, but also to avoid overshooting, which consists either of flying out in front of the opponent, called a "wingline overshoot", or crossing the enemy's flight path, called a "flight path overshoot". The fighter pilot with the most advantageous position is usually above or behind the opponent, and is commonly called the attacker. Conversely, the pilot in the disadvantageous position is usually either below or ahead of the opponent, and is referred to as the defender. Most maneuvers are offensive, such as the "barrel roll attack", "high Yo-Yo", "low Yo-Yo", and "lag roll". Defensive maneuvers more often consist of turning very aggressively to avoid the attacker's guns, with maneuvers like the "break" and the "high Yo-Yo defense"; sometimes tightening the turn, sometimes relaxing it, and other times reversing the turn. The defender will usually maneuver to force an overshoot, or to extend the range enough to dive away and escape. However, other "last-ditch" maneuvers are used by the defender when the attacker achieves a firing solution, or the defender's energy becomes depleted so that maximum turn performance cannot be maintained, such as "guns defense" or the "defensive spiral". History Basic fighter maneuver development began during World War I, with maneuvers such as the "Immelmann", named after German pilot Max Immelmann, the "break" and the "barrel roll". The modern Immelmann differs from the original version, which is now called a stall turn or "Hammerhead turn". The Immelmann turn was an effective maneuver in the early part of the war but as aircraft technology advanced and fighter engines became more powerful, it became a dangerous maneuver, because the opponent could climb and shoot the German fighters when they were almost motionless at the top of the turn. Billy Bishop, the top Canadian ace of World War I, described a break: Watching carefully over your shoulder and judging the