 By late 1935 , Robert Watt 's development of Chain Home ( CH ) radar at Bawdsey Manor in Suffolk on the east coast of England had succeeded in building a system able to detect large aircraft at ranges over 40 miles ( 64 km ) . On 9 October , Watt wrote a memo calling for the construction of a chain of radar stations running down the east coast of England and Scotland , spaced about 20 miles ( 32 km ) apart , providing early warning for the entire British Isles . Development continued , and by the end of 1935 the range had improved to over 80 miles ( 130 km ) , reducing the number of stations required . 
