Question: When was the operational conversion unit of the aerial warfare branch of the Australian Defence Force formed?
Context: No. 228 Operational Conversion Unit was a Royal Air Force Operational Conversion Unit.  It was formed in No. 12 Group at RAF Leeming from Nos. 13 and 54 OTUs in 1947.  The tasking of the OCU was the training of night fighter crews and its aircraft were the De Havilland Mosquito, Gloster Meteor and Gloster Javelin over the years.  The OCU lasted until 1961 at Leeming when it was disbanded. No. 1 Operational Training Unit (No. 1 OTU) was an operational conversion unit of the Royal Australian Air Force (RAAF) during World War II.  Formed in December 1941 at Nhill, Victoria, it relocated to Bairnsdale in mid-1942, and then to East Sale the following year.  No. 1 OTU's primary role was to train aircrew for multi-engined aircraft operations.  At its peak of activity in August 1944, it was operating over 130 aircraft, the most numerous being Bristol Beauforts. Its aircraft and personnel also conducted transport missions in New Guinea and maritime patrols in southern Australian waters.  Following the end of hostilities, the unit was disbanded in December 1945. No. 4 Operational Training Unit (No. 4 OTU) was an operational conversion unit of the Royal Australian Air Force during World War II.  It was formed at Williamtown, New South Wales, in October 1942 to train pilots and wireless air gunners to operate Vultee Vengeance dive bombers.  The school was equipped with Vengeances and CAC Wirraway aircraft.  Accidents were common in operational conversion units, and No. 4 OTU suffered several fatal crashes during its existence.  It was disbanded in April 1944, handing Williamtown over to No. 5 Operational Training Unit. The Royal Australian Air Force (RAAF), formed March 1921, is the aerial warfare branch of the Australian Defence Force.  It directly continues the traditions of the Australian Flying Corps (AFC), formed on 22 October 1912.  The RAAF provides support across a spectrum of operations such as air superiority, precision strikes, intelligence, surveillance and reconnaissance, air mobility, and humanitarian support. An operational conversion unit (OCU) is a unit within an air force whose role is to support preparation for the operational missions of a specific aircraft type by providing trained personnel.  Operational conversion units teach pilots how to fly an aircraft and which tactics best exploit the performance of their aircraft and its weapons.  The Royal Air Force and Royal Australian Air Force, among others, practise this method of training.  The United States Navy calls its units in this role "fleet replacement squadrons". The Australian Defence Force Cadets (ADFC) (Known as the Australian Service Cadet Scheme until 2001) comprises three Australian Defence Force affiliated community-based, youth development organisations of approximately 22,000 cadets and 2,200 cadet staff in 464 units and squadrons across Australia.  Coordination of the Australian Defence Force Cadets is via the ADF HQ unit called Reserve and Youth Division, with Commander ADF Cadets - directly accountable to VCDF.  The ADFC is funded by the Australian Government through the Department of Defence, in partnership with the community. No. 226 Operational Conversion Unit was a Royal Air Force Operational Conversion Unit which was active between 1946 and 1991. Royal Australian Air Force is the aerial warfare branch of the Australian Defence Force. The Defence Force Service Medal (DFSM) is an Australian Military award given for long service by permanent members of the Australian Defence Force.  It is part of the suite of defence force service awards introduced in 1982, which also included the Reserve Force Decoration (RFD, for officers of the Australian Defence Force Reserves) and the Reserve Force Medal (RFM, for non-commissioned members of the Reserve forces).  All three medals were replaced in 2002 with a single medal, the Defence Long Service Medal, which is now awarded to all permanent and reserve members irrespective of rank. No. 231 Operational Conversion Unit was a Royal Air Force Operational Conversion Unit.
Answer: December 1941