Three of the prototypes were delivered to the Army in March 1976 , for evaluation against the rival Boeing - Vertol design , the YUH - 61A .
One was kept by Sikorsky for internal research .
Three of the prototypes were delivered to the Army in March 1976 , for evaluation against the rival Boeing - Vertol design , the YUH - 61A , and one was kept by Sikorsky for internal research .