The paper presents a technical view of the historic ten years from 1935 to 1945 during which operational military radar was developed from the first operational CH stations to the miniature APS-4 airborne ‘podded’ radars which saw operational service at the end of the war. The events leading to the British and German military work are set down, and the principal contributions to wartime radar made from industry and the universities described. The paper ends with a review of the major evolutionary factors which made military radar so important to the Allied war effort during the course of the war.