Following the outbreak of the First World War, Beavis' course at the College was shortened and he graduated in June 1915, top of his class. He was commissioned a lieutenant in the Australian Imperial Force. Assigned to the 5th Field Artillery Brigade, he shipped to the Middle East in November, serving in Egypt during the Sinai and Palestine Campaign before being transferred to the Western Front in April 1916. Initially serving in 4th Field Artillery Brigade, Beavis was promoted to captain in July. In 1917, he attended staff training in England and 2nd Division headquarters before being transferred to 14th Field Artillery Brigade as commander of 53rd Battery. Promoted to major at the time of taking his command, his unit suffered gas attacks in fighting near Ypres but his leadership skills ensured his post remained in Australian hands. The effects of the gas on his health saw him evacuated to England in November. For his actions, he was recommended for the Distinguished Service Order, which was duly gazetted on 14 June 1918. Beavis subsequently returned to his unit and on 21 April 1918, men of his unit were involved in the shooting down of Manfred von Richthofen, the Red Baron. The action was witnessed by Beavis, and in the ensuing investigation as to who shot down the German ace, Beavis placed credit for the kill with his Lewis gunners. He was mentioned in despatches for the second time on 28 May 1918.
Interwar period
Following the conclusion of the war, Beavis remained in England to undertake ordnance and artillery training and in August 1919, married Ethel May Blumer. Following a period of time at Australian High Commission in London, he and his wife returned to Australia in 1922 where he served in a number of staff and regimental positions. In 1928, he once again went to England to attend the Staff College at Camberley. Following his studies, he spent time on the Imperial General Staff, and then was subsequently posted for a second stint in London with the Australian High Commission. In 1936, Beavis was made chairman of the Defence Resources Board which was charged with providing the Australian government with advice on the mobilisation of the Australian industry for war. He repeatedly recommended encouraging development of the private sector in manufacturing prior to the outbreak of hostilities. However, a counterargument that available funds should be prioritised for government factories found greater favour. Following the disbandment of the Defence Resources Board in April 1937, Beavis returned to his regular army duties.
Beavis was promoted to colonel within weeks of the commencement of the Second World War and joined the Second Australian Imperial Force in 1940. He served in the Middle East on the staff of Lieutenant General Sir Thomas Blamey, the commander of the AIF, holding a number of supply related positions. Promoted to brigadier in December 1940, he was successful in a new role of director of ordnance services and was made a Commander of the Order of the British Empire in 1942. Promoted to temporary major general, he returned to Australia to succeed Major General Edward Milford in the position of master-general of the ordnance. He was tasked with co-ordination of private and government manufacturers and producers to provide logistic support for Australia's soldiers, both at home and overseas. As the war came to a close, he found his work becoming more difficult as Australia began to move away from a wartime footing.
