Following initial trials in the early 1960's the US Army purchased 10 Fiat G-91R1's for evaluation in Vietnam, much to the annoyance of the USAF ...After completion of the trials the US Army requested delivery of a new planned G-91YS variant in the planning stages at that time. The USAF strongly objected fearing a rival to the F-5A and intrusion on their own missions sets. This was further exacerbated when the small, powerful, nimble, gun and missile-armed jets achieved some air-to-air kills. South Vietnam also trialed the aircraft but took the F-5 instead after pressure from the USAF and US politicians. The remaining airframes were shipped back to the states for disposal.