Countries worldwide are scrambling to procure medical supplies in response to the COVID-19 pandemic. Several governments have called on non-specialist firms to produce medical ventilators. This column draws three lessons from US munition production in WWII. First, ramping up production takes time, particularly for non-specialist producers. Second, international cooperation is needed to share knowledge on production technology and supply chains. Third, direct public investment in plant expansions should be part of the strategy.