Gyro gunsight

A gyro gunsight (G.G.S.) is a modification of the non-magnifying reflector sight in which target lead (the amount of aim-off in front of a moving target) and bullet drop are allowed for automatically, the sight incorporating a gyroscopic mechanism that computes the necessary deflections required to ensure a hit on the target. The sight was developed just before the Second World War for aircraft use during aerial combat.