The DH Vampire MKI de Havilland Vampire - Wikipedia, the free encyclopedia only got into production in April 45. However the prototype flew in September 43 and even this was delayed by an engine shortage. If needed how much earlier could a service ready Vampire have got into the hands of frontline squadrons. I am thinking if the Me262 had become a real problem in 1944 and was threatening to derail the allies advances into Germany and the RAF was screaming for a counter to the 262.