Rear Admiral Reginald Henderson's 1936 argument linked fighter interception to the time available after an approaching raid was detected. Visual lookouts could struggle to detect fast aircraft early enough for fighters to launch and intercept. British development of beacon-assisted night strikes also gave planners reason to expect opponents to acquire similar capabilities, when aircraft would be harder to see approaching. Designers therefore reserved positions for radar before the equipment was mature. Illustrious became the first carrier fitted with early-warning radar before completion when Type 79Z went aboard. The set needed more power and supporting systems than expected, delaying completion by two months while those additions were fitted.
Notable Point · 8:00-15:14
Radar changes the carrier-defence problem
Illustrious entered service with early-warning radar because visual lookouts could not give fighters reliable warning of fast or night attacks.