Identifying the cognitive processes underlying tactical decision making is vital for two purposes: (a) reducing risk through improved training and (b) facilitating the public's attitudes toward the legitimacy of the police and criminal justice system. Despite this, very little research has been conducted into British police decision making involving the use of firearms. This study begins to address this gap by examining the impact that expertise has on British police's use-of-force decisions during armed confrontations. To do so, the tactical decisionmaking processes of 12 expert specialized firearms officers and 11 novice authorized firearms officers during armed confrontations were compared through cognitive task analysis methods. Data were coded via categories derived from theory and patterns inductively emergent within the data. The results found expert specialized firearms officers to be more flexible in adaptive responding to situational changes, while novice authorized firearms officers reported a more sequential and linear process of tactical decision making. In identifying the key features of expertise within this environment ("adaptive flexibility"), this study has theoretical and practical implications for the acceleration of authorized firearms officers' expertise acquisition to bridge the existing gap resulting from a lack of available qualified operational force commanders.