HACS

Anti-aircraft cruiser HMS Scylla. Her four twin 4.5-inch gun mountings are controlled by the two High Angle Director Towers, one sited behind the bridge and the other abaft the after funnel.

High Angle Control System (HACS) was a British anti-aircraft fire-control system employed by the Royal Navy from 1931 and used widely during World War II. HACS calculated the necessary deflection required to place an explosive shell in the location of a target flying at a known height, bearing and speed.