The military psychiatrist came into existence during World War I as armies dealt with what was then called "shell shock." Over succeeding decades, psychiatrists attempted to find ways of aiding soldiers shaken to the core by combat, often with the goal of not so much curing them as getting them back into the fighting. Their role in modern military organizations has expanded over time to include devising a battery of tests (some bizarre, some commonsensible) for identifying leaders. This fine narrative history deals mostly with British military psychiatry, although it also includes material on the American and continental experiences. The author makes a powerful argument that many military psychological phenomena are culture-bound. The assumption that there is a single post-traumatic stress disorder, he shows, is not merely poor science but hubris.