The Fort Hood Field Unit of the U.S. Army Research Institute for the Behavioral and Social Sciences (ARI) provided support to the TRADOC Combined Arms Test Activity (TCATA) conduct of the Follow-On Evaluation (FOE) of the M9 ACE. The FOE was conducted at Fort Hood, Texas over a 15-week period from March through June 1985, by TCATA for the U.S. Army Operational Test and Evaluation Agency (USAOTEA). This paper describes the human factors assessment support and findings provided to the evaluation by ARI. The primary objective of the assessment was to identify human factors engineering (man-machine) deficiencies that distract from M9 operational effectiveness and maintainability.