WWII Trivia question

What american aircraft design was built and operated by the Japanese during WWII, practically unmodified?
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The KI-61 was loosely based on the ME109, but I think this isn't what you were looking for.
Ki-61. One of the few (maybe even the only ) japanese design with an inline engine. Designed by a german.
You're on a roll! I never heard of the R4D, but it was the Japanese L2D2, allied designation, 'Tabby'! The plane most recognized as the Douglas DC3, or the military C47 Skytrain.