Fittest of the fit was the Royal Navy s boast about its personnel, a claim based on a recruitment process that was effectively self-selection. This book examines that basic assumption and many of the issues that followed from it. Beginning with the medical aspects of recruitment, it looks at how health and fitness was maintained in the adverse environment of sea service, including the particularly onerous extremes of Arctic and Tropical conditions, and life for its submariners and airmen as well as those in the surface fleet. The massive mid-war expansion of personnel was a particular challenge to accepted wisdom and how the Navy coped is a major aspect of the story. Beyond the purely physical, the importance of psychological factors and the maintenance of morale is another theme of the book, taking in everything from entertainment to tolerance of onboard pets. Inevitably, the effects of battle, injury and stress dominated naval medicine, and action experience led to rapid changes in everything from basic preparations to protective clothing. In a conscious search for improvement, the Navy became an early adopter of many medical innovations, driven by a permanent committee created to study personnel issues. To put this all into context, comparisons are made with the other British services as well as US Navy practice. From this emerges a rounded picture of a crucially important factor in the wartime success of the Senior Service. AUTHOR: Kevin Brown is the Curator of the Alexander Fleming Museum at St Mary’s Hospital, Paddington and an expert on the history of medicine. His previous books include Fighting Fit, a history of military medicine in the wars of the twentieth century and Poxed & Scurvied, the story of health and medicine at sea (Seaforth 2011).