English: The Ferranti Gyro Sight Mk I - This type sight calculated target lead (the amount of aim-off in front of a moving target) and bullet drop automatically. The pilot/gunner had to look into the narrow field folded prismatic telescopic sight at the top of the device. The sight incorporating a gyroscopic mechanism that computed the necessary deflections required to ensure a hit on the target. It saw limited production in the spring of 1941, with the sights being first used operationally against Luftwaffe raids on Britain in July the same year. The Mark I sight had a number of drawbacks however, including a limited field of view, erratic behavior of the reticle, and requiring the pilot/gunner to put their eye up against an eyepiece during violent maneuvers. Production of the Mark I was postponed and work started on an improved sight. It was replaced by the Mark II which incorporated a reflector sight, allowing the pilot to view through the sight at a more comfortable (and safer) distance.