In 2020, the world was hit by a global pandemic through COVID-19, causing millions of deaths worldwide. The last two years proved that a health-related crisis like COVID-19 strains us as a society and the capacities of health systems worldwide. Severe infections of COVID-19 require higher capacities of hospital beds, ICUs with ventilators and Personal Protective Equipment. For health systems, the question arises of how to secure enough PPE and ventilators before and during a health-related crisis like COVID-19. This research explores how health systems can create responsive and prepared supply strategies to meet the rising demand for critical medical supplies during health-related crises. Concerning the availability of critical medical supplies, preparedness entails stockpiling as a supply strategy. Furthermore, preparedness entails actions decision-makers in health systems can take to increase the effectiveness of responsive supply strategies. Responsiveness refers to supply strategies used at the beginning of a health-related crisis in the short term. Responsive supply strategies include ramping up domestic production, supporting innovations, loaning medical supplies, and purchasing medical supplies from the world market or through direct tender. In this research, a System Dynamics model was developed to explore how health systems can create resilient and responsive supply strategies, a System Dynamics model was developed, focusing on the English health system as an example for the Global North. Given the deep uncertainties surrounding the supply chain of critical medical supplies, Exploratory Modelling and Analysis was conducted to identify candidate policies and explore their performance given the uncertainties. Specifically, uncertainties affecting the success of purchasing supplies through direct tender and from the world market had the most impact on the availability of PPE and ventilators. The results of the analysis and the findings in the literature provide the following recommendations to decision-makers in health systems to create prepared and responsive supply strategies that ensure the availability of critical medical supplies during health-related crises. Decision-makers can implement (i) stockpiles exhibiting higher inventory levels than recommended, and no delays concerning the operation within the warehouse or the delivery of the medical supplies. Furthermore, it is suggested to (ii) implement diverse supplier frameworks and crisis frameworks, (iii) diversify supplier, (iv) implement stocks of raw material for domestic production. It is useful for decision-makers to apply several responsive supply strategies simultaneously. Furthermore, health systems can further investigate additional supply strategies. In this research, it is assumed that collaboration is not relevant nor of interest for the English health system. Hence, it would be interesting to explore the effect that sharing critical medical supplies between national health systems could have on the shortage of PPE and ventilators in the future.