If Frank Whittle's jet concept had been funded in 1928, how early could jets have affected World War II?
Short answerThe prerequisite technology would still take work, but successful early investment might put British jet aircraft into service from about 1936-37 onward.
NotesA jet engine depended on much more than the original idea: materials, aerodynamics, and production capacity all had to mature. Earlier financial support could accelerate experimentation without eliminating those engineering constraints. In a favorable scenario, Britain might field jet aircraft around 1936 or 1937. It could then enter World War II with a second generation already under development rather than treating jets as a late-war innovation.