In 1937, Bowen's team set their crude ASV radar, the world's first airborne set, to detect the Home Fleet in dismal weather.[20] Only in spring 1939, "as a matter of great urgency" after the failure of the searchlight system Silhouette,[21] did attention turn to using ASV for air-to-air interception (AI).[21] Demonstrated in June 1939, AI got a warm reception from Air Chief Marshal Hugh Dowding, and even more so from Churchill.
This proved problematic.[21] Its accuracy, dependent on the height of the aircraft, meant that CH, capable of only 4 sm (0.0068 km), was not accurate enough to place an aircraft within its detection range, and an additional system was required.[22] Its wooden chassis had a disturbing tendency to catch fire (even with attention from expert technicians),[23] so much so that Dowding, when told that Watson-Watt could provide hundreds of sets, demanded "ten that work".[24] The Cossor and MetroVick sets were overweight for aircraft use[21] and the RAF lacked night fighter pilots, observers,[25] and suitable aircraft.[26][page needed]