Venom from Vampire
The prototype Venom was converted from an early Vampire 1. Essential differences were wing (slight sweep back) and engine (Ghost in place of Goblin). As the aircraft was developed the differences got more and more pronounced. Probably about as much commonality at the end of the process as there was between a Spitfire I and a Spitfire 24. For DH it was essentially a fairly incremental process of improvement of the basic product providing additional range and capability, as well as developing navalised versions and two seat trainers and night fighters to a higher degree than Vampire.