Major General John William Alexander O'Brien, DSO (13 June 1908 – 27 May 1980) was a senior officer in the Australian Army during the Second World War.

[3] Australia had compulsory military training at this time, and O'Brien served in the Australian Army Cadets at St Patricks' and then in the Militia.

A letter of introduction from Thomas Blamey, the Chief Commissioner of Victoria Police enabled him to obtain a work permit for the United States, and secure a position with the American Bridge Company in Gary, Indiana.

He spent four days at the United States Army Field Artillery School at Fort Sill, Oklahoma, and toured the American Civil War battlefields in Virginia.

[11] On 1 September 1939, O'Brien became a full-time soldier as Deputy Assistant Director of Artillery (DADA) at Army Headquarters in Melbourne.

When the government announced in February 1940 that it was raising the 7th Division for overseas service, O'Brien decided to join the Second Australian Imperial Force (AIF).

His application was supported by Brigadier Cyril Clowes and Lieutenant Colonels Edward Milford, Charles Lloyd, all of whom were regular officers, and all of whom were appointed to commands in the 7th Division.

The choice of replacements was limited to majors already in the Middle East, and the Commander Royal Artillery (CRA), 7th Division, Brigadier Frank Berryman, selected O'Brien.

[24] O'Brien noted that the 25-pounder, while a superb weapon, was unsuitable for use in mountainous or jungle terrain due to the difficulty in transporting it.

[8] As the tide of war turned in favour of the Allies, the government directed that production of munitions be reduced, allowing resources to be diverted to other uses, and avoiding the creation of stockpiles of unwanted items.

While he believed that the Owen Gun was a superior weapons based on its performance in trials, he deferred a decision until reports came in from the field.

[28] O'Brien and the Engineer-in-Chief, Major General Clive Steele, left Melbourne on 5 August 1944 on a tour of ordnance plants in the United States, Canada and Britain.

In London, O'Brien was invested with his membership of the Distinguished Service Order by George VI in a ceremony at Buckingham Palace.

[30] As such, he worked closely with both the British Commonwealth Occupation Force and headed the Science and Technology Division of the Economic and Scientific Section at the headquarters of the Supreme Commander for the Allied Powers.

[31] In October 1948, he was appointed the president of a military court convened to try Admiral Soemu Toyoda, the former commander of the Japanese Combined Fleet.

[33] The post in Tokyo gradually became a sinecure, and O'Brien had time to produce a book, Guns and Gunners (1950), on the wartime deeds of the 2/5th Field Regiment.

[36] When the Washington posting came to an end in June 1954, O'Brien and his family took a tour of Europe before sailing from Southampton for Australia on the SS Orcades on 8 August.

[37] In April 1955 he became the director of engineering and sales with Howard Auto-Cultivators Pty Ltd, a Sydney firm that made rotary hoes.

When no buyer was found, O'Brien bought it himself, setting up a new business, Contract Tooling Pty Ltd (CTPL), on 27 August 1959.