Although quite a few strategic documents had warned about the threat of a pandemic in Spain, when COVID-19 first appeared in 2020, it caught the Spanish authorities almost by surprise. An exceptional measure was quickly introduced with the decree of a state of alarm, and the country’s armed forces were given an especially prominent role with regard to auxiliary work. These decisions were made against the backdrop of two particular features that characterize Spain. Firstly, its society is, in general, apprehensive of issues related to defence and, in particular, there is little sympathy towards the domestic deployment of the armed forces. Secondly, since 2007, the Military Emergencies Unit (UME)—a specialized military corps trained to act quickly and autonomously in the face of natural disasters at home and abroad—has been operational. Despite the lack of organizational preparedness on the part of political leaders and societal hesitation about military action on national territory, the final result was highly satisfactory. This study explains: 1) the legal and institutional framework that, despite the initial lack of readiness, was able to act quickly and efficiently; 2) the actions that constituted the military response and the way in which the structure of the joint operational command and existence of the UME played a crucial role in the success of the operation; and 3) the positive impact in the media and society resulting from this deployment.