Although a part time officer and nearly 50 years of age, Monash was given command of an infantry brigade (4th) that went to Egypt early in 1915 under ANZAC, a combination of Australian and New Zealand forces. The time the brigade spent in Egypt, was not wasted, but spent in training to Monash’s rigid ideas. He was sent to Gallipoli where he served with dedication to the very best planning possible under difficult circumstances.
In 1916 he was given command of a division (3rd) which went on to greatly influence the outcome of the major events at Messine and Passchendaele. During this period of his service it was found that he personally communicated exceptionally well with other senior commanders such as Plumer and Haig. Many of his successes were attributed to his ability to communicate effectively at all levels of command.
In 1918 he succeeded Birdwood as Australian Corps commander, at this time there was political rumbling because he was not considered a professional soldier but undeterred he continued with his usual meticulous planning. He was committed to utilising any equipment which might prevent unnecessary waste of lives, such as tanks and sought improved ways to use machine-guns and smoke screens. Tank warfare in conjunction with infantry was changed by Monash and used with great success in 1918 at the Battle of Hamel, these methods were later used through out the Allied armies.
At the end of the war Monash took the post of Director General of Repatriation and Demobilisation for Australia which was based in London and he did not return to Australia until late in 1919. A number of honours were bestowed on him by the countries of Belgium, France and Britain.