From the Publisher:
On 10 May 1940, the Wehrmacht launched its assault on the West. One element of the West’s response was the dispatch of RAF Bomber Command ‘heavy’ bombers at night over German industrial centers. These raids had only limited effectiveness, but the inability of the Luftwaffe to chase down RAF bombers at night so annoyed Wolfgang Falck that it swiftly resulted in the creation of a credible night fighter force.
Initial trials had been flown with Bf 110s at dusk in Denmark on April 1. Nachtjagd Division was founded in the summer of 1940. Its first few months were chaotic, with constant reorganizations of units, and reassignment of aircraft, but soon enough the night fighter arm was achieving steady victories—and losing crews at a similarly steady rate.