Subsequent to the reforms brought about in the Indian Army by Lord Kitchener in 1903, the regiment's designation was changed to 40th Pathans. In 1904, the 40th Pathans proceeded to Tibet as reinforcements for the Tibet Mission Force. On the outbreak of the First World War the regiment was stationed in Hong Kong. It arrived in France on 2 April 1915, and within days, was on the frontlines. The 40th Pathans fought with great gallantry in the Second Battle of Ypres, where they suffered 320 casualties on 26 April, and in the Battles of Aubers Ridge and Loos. In December, the regiment left for East Africa, where they served till February 1918, and again distinguished themselves in the long and bitter campaign. The 40th Pathans suffered a total of 800 casualties (killed or wounded) during the war, while 1066 officers and men were invalided out of service due to sickness. In 1919, the 40th Pathans participated in the Third Afghan War.