Born in Essex, Petre forsook his early legal career to pursue an interest in aviation, building his own aeroplane and gaining employment as an aircraft designer and pilot.

The following year, he chose the site of the country's first air base at Point Cook, Victoria, and established its inaugural training institution, the Central Flying School, with Eric Harrison.

Shortly after the outbreak of World War I, Petre was appointed commander of the Mesopotamian Half Flight, the first unit of the newly formed Australian Flying Corps to see active service.

[2][3] Impressed by Louis Blériot's pioneering cross-channel flight in July 1909, Petre gave up his legal practice, borrowed £250, and proceeded to build his own aeroplane, with design assistance from his brother Edward, an architect.

[4][6] Uninjured and undiscouraged, he borrowed a further £25, took flying lessons at Brooklands Airfield in Surrey, and obtained Royal Aero Club Aviator's Certificate No.

[2][4] Characterised by official Royal Australian Air Force (RAAF) historian Douglas Gillison as "quiet and academic by nature",[7] and coming from a long line of Catholic clergy, Petre was nicknamed "Peter the Monk".

[8] On Christmas Eve 1912, Edward Petre, who was known as "Peter the Painter", was killed in an accident at Marske-by-the-Sea, Yorkshire, while attempting to fly from Brooklands to Edinburgh.

[5] In December 1911, the Australian Defence Department had advertised in the United Kingdom for "two competent mechanists and aviators" to establish a flying corps and school.

[6] Eight days later Petre registered Australia's first military flying accident when he crashed a Deperdussin while trying to avoid telephone wires during landing; he escaped with bruising but the plane was wrecked.

The four students included Captain Thomas White and Lieutenants Richard Williams, George Merz, and David Manwell; Harrison was responsible for initial training and Petre for advanced instruction.

Petre was appointed the Half Flight's commanding officer and embarked for Basra via Bombay on 14 April, later to be joined by fellow pilots White, Merz and Lieutenant William Treloar, along with thirty-seven ground staff.

[14][15] In Mesopotamia, Petre was required to lead the AFC contingent in reconnaissance and sabotage missions, and had to deal with unreliable machines, hazardous terrain, and the threat of incarceration or death at the hands of hostile tribesmen.

The squadron moved into Kut following the city's capture by the Allies during the Battle of Es Sinn in September;[18] for his part in the operation, Petre was again mentioned in despatches.

[15][17] Around the time of the Battle of Ctesiphon in November, he devised an implement shaped like a small garden rake that allowed him to accurately measure ground distances from the air to better map the desert terrain.

In his volume on the Air Force for The Australian Centenary History of Defence in 2001, Alan Stephens noted that Petre made "the greater contribution to the establishment of Point Cook and the Central Flying School", concluding that "perhaps any judgement would not only be moot but also gratuitous, as by circumstance and achievement both men properly belong in the pantheon of the RAAF".