In March 1939, Robertson was appointed commander of the 7th Military District, which encompassed the Northern Territory. It was his first command since the First World War. He was promoted to the temporary rank of colonel in August 1939, and this became substantive in November. The job involved cooperation with the Royal Australian Navy and Royal Australian Air Force, and the administration of a company of regular soldiers known as the Darwin Mobile Force. After the Second World War began in September 1939, Robertson became responsible for supplying the 7th Military District's quota of volunteers for the Second Australian Imperial Force (AIF). A strike on the waterfront saw Robertson committing troops to help unload cargo.