Fast and frugal heuristics have been used to model decision making in applied domains very effectively, suggesting that they could be used to improve applied decision making. We developed a fast and frugal heuristic for infantry decisions using experts from the British Army. This was able to predict around 80% of their decisions using three cues. Next, we examined the benefits of learning to use the fast and frugal heuristic by training junior officers in the British Army to apply the heuristic and assessing their accuracy and mental workload when making decisions. Their performance was compared to a control condition of junior officers who applied standard military decision methods. Participants using the fast and frugal heuristic made decisions as accurately as participants in the control condition, but with reduced mental demand. This demonstrates that fast and frugal heuristics can be learnt and are as effective as analytic decision methods.