The Me110 was intended to be the elite "zerstorer" of the Luftwaffe. But although fast and well-armed, it was not very maneuverable and was a disappointment in the long-range escort fighter role. However, the scheduled replacement for the Me110, the Me210, was such a complete lemon that it was decided to sell them to the Hungarians and give the old 110 a makeover. The new Zerstorers weren't much better than the old ones, but they provided useful service as fighter-bombers and night fighters.
Cool stuff for Bf110 lovers: