The Distinguished Service Medal was the main gallantry medal given to naval ratings during the First World War, with over 4,000 medals being awarded. The citations for these awards are difficult to identify in surviving documents, which has meant that the reason why many of the awards were made has remained somewhat enigmatic. For the first time this book documents all the surviving recommendations for these awards as well as providing analysis of the campaigns for which the awards were made. The posthumous recommendations for the medal and also details of the other awards made to DSM recipients are included to provide a definitive history of the medal during the First World War and the Interwar period.