 The crews were bound to get lucky eventually , and this came to pass on the night of 22 / 23 July 1940 , when a Blenheim IF of the FIU received direction from the Poling CH station and picked up the target at 8 @,@ 000 feet ( 2 @.@ 4 km ) range . The CH radar operator directed them until the observer visually spotted a Do 17 . The pilot closed to 400 feet ( 120 m ) before opening fire , continuing to close until they were so close that oil spewing from the target covered their windscreen . Breaking off , the Blenheim flipped upside down , and with no visibility the pilot didn 't recover until reaching 700 feet ( 210 m ) . The target crashed off Bognor Regis , on the south coast of England . This was the first confirmed successful use of airborne radar known to history . 
