Hi Krakatoa
In the United States, the National Advisory Committee for Aeronautics (NACA) noted in 1920 that air-cooled radials could offer an increase in the power-to-weight ratio and reliability, and by 1921 the U.S. Navy had announced it would only order aircraft fitted with air-cooled radials while other naval air arms followed suit
I think that's why...
Regards,
Adam
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