Motivation – To understand the factors acting upon decision making of military planners prior to the introduction of digital planning systems. Research approach – Participant-observation by the research team and direct observation of the planning process on exercises. Findings – Many different disciplines contribute to the planning process in a co-operative and collaborative manner. Each stage in the planning process results in a further set of constraints being applied, each of which offer successive refinement of the plan. Research limitations/Implications –The research is limited to land-based military planning. Originality/Value – This research is based on field observation of military planners with tight deadlines and a non-compliant opposing force. Take away message – ‘Military planning seems to be more about identification of relevant constraints than optimization of decisions’ .