This article illuminates the little‐known high‐command experiences of Henry Horne. Drawing predominantly upon his (largely unused) papers, it identifies three major preoccupations – ambition, optimism and religiously‐based moral outrage – behind his mentality, and contends that these concerns contributed significantly to his daily exercise of command. While addressing current debates about command, the article also discusses Horne's reactions to perceived German atrocities – an issue generally overlooked in other studies – and suggests that, rather than pursuing a ‘depersonalised’ approach to the investigation of First World War generalship, more attention must be given both to this subject and to the complex mentalities behind command decisions.