Hobbs was gazetted to the Royal Engineers in 1898. He served in the Boer War (1899–1902), the Somaliland campaign in 1903 and in the Gold Coast in 1904–05. From 1907–11, he was technical supervisor at the School of Musketry. He returned to the field in the First World War, serving as assistant adjutant and quartermaster general in France and Italy until February 1918.