I'd say that there
were returns, but only for the Allies after the war.
Like many things, the GUPPY fleet boat conversion was heavily influenced by the Type XXI. It still amazes me how much we benefited in aviation, rocketry, and submarine technology by going through Germany's production and drawing board designs after the war.
Compare the
P-59 with the
Me-262 , for example. Not even in the same ballpark. Scary, is it not?