The USAAF had a "operational" (I use the term loosely) Helo called the R-4 in at least 1943 (as far back as I can document on short notice.
from AAF:
R-4 : Designer: Sikorsky. Main rotor with 3 15ft blades. Engine: Warner 180hp. Approx speed: 90-100 mph. Weight: 2500 lbs. Length: 48 ft. Approx. range: 100 miles. Crew: 2. First sucessful flight: 13 Jan. 1942.
The theroy in 1944 was that the Helocopter would be useful in Liason, Recon, and Rescue rolls. Whitch brings up the point: If we could get one in AH, What would we do with it?

(don't get me wrong, though, I think it would be neat.)
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332nd Flying Mongrels"When in doubt, put a few more rounds into it."