Using the same criteria as that employed to assess imperial interoperability in Chapter 3, this chapter examines how Britain, India, and the dominions raised their armies and worked together during the Second World War. It finds that, in spite of some terrible defeats, such as Singapore and Dieppe, and some difficult personal relationships between generals, the armies of the empire worked quite well together. This owed much to decades of common training, organization, and staff procedures. The ability of the empire’s armies to work together contrasts sharply with the inability of any of them to work smoothly with American formations, as the South Africans discovered in Italy and the Australians discovered in the Pacific. The Americans spoke a different staff language than the one that the armies of the British Empire had learned over the four-plus decades of the imperial army project.