Kerrison Predictor - US Service

US Service

Because the U.S. Army Coast Artillery Corps was not satisfied with the Army's 37mm Gun M1, in September 1940 General George C. Marshall asked the British for the loan of four Bofors 40 mm guns with Kerrison Predictors for testing.

During testing the Kerrison Predictor provided accurate fire control to a range in excess of 1,500 m (4,900 ft), and the Bofors gun was reliable, and in fall 1940, the Ordnance Department standardized the Kerrison Predictor for use with the 37 mm gun. By February 1941, the U.S. Navy had adopted the Bofors for use on their ships. To ease production problems, the Army reluctantly standardized on the 40 mm in February 1941; the U.S. was building the Bofors for the British under the Lend-Lease Program.

The Predictor's plans were passed to Sperry, who were just commencing production of their own complex high-altitude system, the M7 Computing Sight, and had no excess capacity to produce the new design as well. Instead, they completed changes needed to U.S. production and sent the plans back to the Army for production elsewhere and in December 1940 the Singer Corporation was contracted to produce 1,500 predictors per month to equip the Army's existing 37 mm guns while production of the 40 mm Bofors was ramped up. Singer required massive changes in the company, including building new factories and the switching of a foundry from steel to aluminum and production did not begin until January 1943, but the entire order was filled for the M5 Antiaircraft Director by the middle of 1944. For a brief time, some of the U.S. Army's Bofors guns were equipped with the Sperry M7, but these were replaced in the field as soon as M5s became available.

With aircraft speeds increasing dramatically during the war, even the speed of the Kerrison Predictor proved lacking by the end. Nevertheless, the Predictor demonstrated that effective gunnery required some sort of reasonably powerful computing support, and in 1944 Bell Labs started delivery of a new system based around an analog computer. The timing proved excellent. Late in the summer the Germans started attacking London with the V-1 flying bomb, which flew at high speeds at low altitudes. After a month of limited success against them, every available anti-aircraft gun was moved to the strip of land on the approach to London, and the new sights proved to be more than capable against them. Daytime attacks were soon abandoned.

Long after the war, U.S. M5's started appearing in surplus shops in the late 1950s. John Whitney purchased one (and later a Sperry M7) and connected the electrical outputs to servos controlling the positioning of small lit targets and light bulbs. He then modified the "mathematics" of the system to move the targets in various mathematically controlled ways, a technique he referred to as incremental drift. As the power of the systems grew they eventually evolved into what is today known as motion control photography, a widely used technique in special effects filming.