Royal Air Force Sector Clocks

“Colour Change Clocks”

Originally known as "colour change clocks," Sector Clocks were first used during World War I by the Royal Flying Corps to plot movements of incoming German aircraft. During World War II, Sector Clocks played a significant role in the Battle of Britain, the Blitz, and the bombing of British cities that followed by allowing the British to hold control of the sky with fighters ready to intercept enemy aircraft within five minutes of initial contact.

The dial of the Sector Clock is ringed with red, yellow, and blue triangles, each representing a five-minute segment. Two numerical rings - an outer 12-hour dial and an inner 24-hour dial, frame the triangles.

Read more at: https://sandiegoairandspace.org/collection/item/wwii-raf-sector-clock

Source: https://sandiegoairandspace.org/collection/item/wwii-raf-sector-clock