Well, if whe are to go down the line with who made what, the 1st jet engine ever created was made by a romanian : Henri Coanda.
To keep it short, here are the relevant achievements :
-1910 : the first thermojet aircraft
-1926 : the Coanda effect
So, it wasn't a german or an american researcher, it was a romanian, and it didn't happen at the fall of WW2, but before WW1.