Unit Colour Patches are worn on the Slouch Hat

Slouch hat

A slouch hat is a wide-brimmed felt or cloth hat with a chinstrap, most commonly worn as part of a military uniform. It is a survivor of the felt hats worn by certain 18th century armies. Since then, the slouch hat has been worn by military personnel from many nations including Australia, Britain,...

 in the Australian Army

Australian Army

The Australian Army is Australia's military land force. It is part of the Australian Defence Force along with the Royal Australian Navy and the Royal Australian Air Force. While the Chief of Defence commands the Australian Defence Force , the Army is commanded by the Chief of Army...

 to indicate which unit they are from.
Unit colour patches are approximately 40mm x 40mm in size and have a large variety of colours and shapes on them.

While some are recent creations many date back to World War I

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

, when on 8 March 1915 1 Division

1st Division (Australia)

The 1st Division is the main formation of the Australian Army and contains the majority of the army's regular forces. Its headquarters is in Enoggera, a suburb of Brisbane...

 Order No 81 was issued at Mena

Mena

-Biology:*Mena, one of three members of the Ena/Vasp homology proteins in mice*Mena , a genus of sea anemone-Geography:*MENA, an acronym for the "Middle East & North Africa" region**For coverage of the MENA revolutions see Arab Spring...

, Egypt

Egypt

Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...

 authorising their creation.

The original series of colour patches was discontinued in 1949, and a new system was introduced in 1987 known as Series I and Series II colour patches. The Series I range are known as the 'Heritage' patches and are the pre-1949 patches maintained in a register with the Series I 'Extended' and Series II range introduced during the 1990s.
Both are used in the Australian Army due to some units tracing their lineage to the 1st AIF

First Australian Imperial Force

The First Australian Imperial Force was the main expeditionary force of the Australian Army during World War I. It was formed from 15 August 1914, following Britain's declaration of war on Germany. Generally known at the time as the AIF, it is today referred to as the 1st AIF to distinguish from...

 units. The Register also includes the patches for the Royal Australian Air Force

Royal Australian Air Force

The Royal Australian Air Force is the air force branch of the Australian Defence Force. The RAAF was formed in March 1921. It continues the traditions of the Australian Flying Corps , which was formed on 22 October 1912. The RAAF has taken part in many of the 20th century's major conflicts...

 and Royal Australian Navy

Royal Australian Navy

The Royal Australian Navy is the naval branch of the Australian Defence Force. Following the Federation of Australia in 1901, the ships and resources of the separate colonial navies were integrated into a national force: the Commonwealth Naval Forces...

patches.