From Wiki:
During
World War II, the
United States Army Air Force 63d Bombardment Squadron, assigned to the
Fifth Air Force 43d Bombardment Group, flew
B-17 Flying Fortresses from the airfield between 15 June-3 August 1942.
Other USAAF units assigned to Charleville were the 8th and 480th Service Squadron of the 45th Service Group.
Charleville was also the western terminus of the
Air Transport Command Pacific Wing (later Division).
The
Royal Australian Air Force (RAAF) had a unit at Charleville. No 15 Operational Base Unit provided support services for transiting aircraft, such as refuelling or minor maintenance.
So, hardly 'secret'.