In March 2020, epidemiological modelling of COVID-19 predicted overwhelming demand on healthcare resources, yet data that emerged painted a different picture. Our management science health systems team at the University of Strathclyde collaborated with one NHS organisation to contextualise national policy and predict local resource needs before the pandemic took hold. Using action research, we combined organisational expertise, local and international data, and healthcare systems expertise to create a discrete event simulation model that predicted concurrent resource use over the first 10 weeks of the pandemic with realistic estimates of uncertainty. This allowed the organisation to create an effective strategy for resource planning. Had they followed national guidance, the costs would have been unwieldy and futile. Our decentralised approach delivered valuable information in a timely manner. This case study is unique in healthcare literature and serves as an example of successful methodology for similar crises.