Abstract: Before modernizing any information-intensive system, it is important to understand how people are performing their jobs using that system. This understanding is built not simply by observing what people are doing, but by digging into how people think about their jobs, what coordination they need to do, and the dependencies among subtasks that together dictate a workflow. Building a thorough understanding of complex tasks takes weeks or months rather than days, but we needed to get as much of an understanding as possible in three days of a real-time command and control centre for military unmanned vehicles. To help structure our investigation, we used a technique called Applied Cognitive Task Analysis (ACTA) [14]. To the best of our knowledge, ours is the first use of ACTA to study a military command and control centre in such a time-compressed fashion. We describe our application of ACTA and the types of recommendations we were able to generate from our analysis, and provide reflections on the study process. Another contribution of this paper is based on the fact that we were able to gain access to a facility that is not usually open to researchers; hence the ACTA results may be of interest to those who would benefit from knowing about the major cognitive challenges facing members of the Predator Unmanned Aircraft System community.