 Bowen led a series of lectures at Bentley Priory, on the theory of radar guided night interception and concluded that the fighter would require a speed advantage of 20 to 25 % over its target. The main Luftwaffe bombers — the Junkers Ju 88, Dornier Do 17Z, and Heinkel He 111 — were capable of flying at about 250 miles per hour (400 km / h), at least with a medium load. This implied a fighter would need to fly at at least 300 miles per hour (480 km / h) and the Blenheim, fully loaded, was capable of only 280 miles per hour (450 km / h). Bowen's concerns over the poor speed of the Blenheim were proved right in combat.
