Early SD and SI radar fits were search systems rather than fire-control equipment. Their most important purpose was to warn a surfaced submarine of approaching aircraft early enough to dive. They could also contribute to surface search and helped prepare crews for radar-assisted attacks by 1941. Because a submarine's aerial was close to sea level, its radar horizon was far shorter than that of a carrier or other large surface ship. Radar could therefore offer Britain more immediate operational value than a snorkel in its expected theatres.
Notable Point · 27:47-29:10
Early radar gave British submarines warning and search reach
British submarine radar installations emphasized warning of aircraft while also offering limited surface-search capability.