After his move to the Indian Army, following the end of the First World War, Slim first joined the 1st Battalion of the 6th Gurkha Rifles (1/6GR). Though initially received with reserve, having been appointed to the Battalion rather than selected by 6GR, he quickly earned the trust and respect of both officers and men through his hard work, professionalism and approachability. This respect was shown by his appointment, in 1921, as the Battalion’s Adjutant.
Slim remained with the Battalion until 1924, after which he attended the Indian Army Staff College at Quetta, where he was the top-placed student. Such stellar performance at Quetta, inevitably meant that staff appointments followed and Slim was to serve at Army Headquarters India, at the Army Staff College at Camberley, at the Imperial Defence College and at the Senior Officers School in Belgaum. In his time, and until the outbreak of the Second World War, he returned to regimental soldiering only briefly, as a Company commander back in 1/6 GR and for a year as Commanding Officer in 2nd Battalion 7th Gurkha Rifles (2/7GR).
During this period, Slim not only greatly enhanced his skills in military strategy, but began seriously to write, mainly in the form of short stories and articles, under the pen name of Anthony Mills. As well as honing his skills as a writer, one of the few strengths for which he had been noted at school, this provided a secondary income to support his growing family. Perfecting his natural storytelling abilities also furthered his talents at clearly expressing his ideas and aims to others, something that was to serve him well as he rose through the ranks to higher command.