The Sikorsky-designed R-6A two-seat observation helicopter was a refined version of the R-4, the first AF helicopter to serve in a combat zone. First flown in Oct. 1943, the R-6A used the same rotor and transmission system as the R-4 but it had a more powerful Franklin engine. With its fuselage completely redesigned to reduce air resistance and improve pilot visibility the R-6A bore little resemblance to its boxy-looking predecessor. This example is on display at the National Museum of the USAF.