Catholic chaplaincy has been provided for Australians serving in the military since the 1901 contribution of forces to fight in the Boxer Rebellion.

The following individuals have been elected as Bishop of the Armed Services:[2] Army and Air Force have three Principal Chaplains; one each to represent Catholicism, Anglicanism and nonconformist Protestantism.

Catholic priests who are promoted to Principal Chaplains of the ADF are traditionally nominated for and receive the title monsignor from the Pope.

Chaplains are charged with the responsibility to care for the religious, spiritual and pastoral (welfare) needs of Defence members and their families.

Chaplains, especially those appointed to training establishments, conduct classes on ethics, morals, values and character development with their military units.

It is possible for a priest or deacon to be ordained solely into (incardinated) the Defence Diocese/Military Ordinariate and thus he fully belongs to the Military Diocese for life.