 Another command , established under emergency conditions when a convoy intended for supply of the Philippines , known as the Pensacola Convoy , was rerouted to Brisbane due to the attack on Pearl Harbor . Brigadier General Julian F. Barnes was ordered to assume command of all troops in the convoy on 12 December 1941 concurrent with their designation as Task Force — South Pacific , and place himself under the command of MacArthur . The next day , by radiogram , the Chief of Staff of the United States Army , General George C. Marshall , ordered Barnes to assume command as Commander , US Troops in Australia and take charge of all troops and supplies . On 22 December 1941 , with the convoy 's arrival in Brisbane , the command was designated as United States Forces in Australia ( <unk> ) . It was renamed U.S. Army Forces in Australia ( USAFIA ) on 5 January 1942 . Its mission was to create a base in Australia for the support of the forces still in the Philippines . 
