The Kerrison Predictor was one of the first fully automated anti-aircraft fire-control systems. It was used to automate the aiming of the British Army's Bofors 40 mm guns and provide accurate lead calculations through simple inputs on three main handwheels.

The predictor could aim a gun at an aircraft based on simple inputs like the observed speed and the angle to the target. Such devices had been used on ships for gunnery control for some time, and versions such as the Vickers Predictor were available for larger anti-aircraft guns intended to be used against high-altitude bombers. Kerrison's analog computer was the first to be fast enough to be used in the demanding high-speed low-altitude role, which involved very short engagement times and high angular rates.

The design was also adopted for use in the United States, where it was produced by Singer Corporation as the M5 Antiaircraft Director, later updated as the M5A1 and M5A2. The M6 was mechanically identical, differing only in running on UK-style 50 Hz power.

By the late 1930s, both Vickers and Sperry had developed predictors for use against high-altitude bombers. However, low-flying aircraft presented a very different problem, with very short engagement times and high angular rates of motion, but at the same time less need for ballistic accuracy. Machine guns had been the preferred weapon against these targets, aimed by eye and swung by hand, but these no longer had the performance needed to deal with the larger and faster aircraft of the 1930s.

The British Army's new Bofors 40 mm guns were intended as their standard low-altitude anti-aircraft weapons. However, existing gunnery control systems were inadequate for the purpose; the range was too far to "guess" the lead, but at the same time close enough that the angle could change faster than the gunners could turn the traversal handles. Trying to operate a calculating gunsight at the same time was an added burden on the gunner. Making matters worse was that these ranges were exactly where the Luftwaffe's dive bombers, which were quickly proving to be a decisive weapon in the Blitzkrieg, were attacking from.

The problem was taken up by Major A.V. Kerrison of the British Army, who had been working as the Army liaison at the Admiralty Research Laboratory, Teddington, through 1930s. Kerrison had worked on several of the Royal Navy's gunnery computers and took up the problem in the late 1930s. After the war, Kerrison went on to become Director of Aeronautical and Engineering Research at the British Admiralty.

His solution was a calculator that dispensed with many of the corrections and timing issues seen in devices like the Vickers Predictor which were intended for high-altitude fire. Instead, it made a relatively simple calculation of the impact point based on relative motion as provided by the operator. Key to the concept was the use of two ball-and-disk integrators, used in this case to maintain a constant rate of motion. On top of the motorized disk were two metal balls, set one on top of the other with the bottom one in contact with the disk and the second in contact with mechanisms that drove the Predictor's laying handwheels.

The two balls were clutched so they could be separated or forced together. For the initial setup, the operator would declutch the balls and use the handwheels to bring the Predictor's telescope onto the target. This also moved the two balls across the surface of the disk, although they were not in contact with it. Once they had begun tracking it, the clutch would be moved to bring the two balls into contact with the disk, at which point the rotation of the disk would cause the balls to rotate and thus automatically move the telescope to stay aligned with the target.