The U.S. Air Force MH-139A Grey Wolf helicopter by Boeing [BA] attained initial operational capability (IOC) on Aug. 10 in the planned replacement of the service's UH-1Ns by Bell [TXT] for missile field security, Air Force Global Strike Command (AFGSC) said on Monday.The 908th Flying Training Unit at Maxwell AFB, Ala., is to become the formal training unit for the MH-139A. The Air Force has 38 MH-139As on contract, and, in June last year, the service said that it finished…