The Governments of Australia and the United States have concluded that Article IV of their mutual defense treaty applies to the terrorist attacks on the United States.
The United States welcomes Australia's decision to join us in applying the ANZUS Treaty, which serves to reinforce the strong bonds of friendship and shared values that unite the American and Australian people. The tragic events of September 11, 2001 took place just one day after President Bush and Prime Minister Howard stood together in Washington, D.C. to commemorate the 50th anniversary of the U.S.-Australia alliance. Although our alliance with Australia was crafted under very different circumstances than exist now, the events of September 11, 2001 are a powerful reminder that the alliance and our shared commitments are no less valid today.
Australia shares our assessment of the gravity of the situation and is resolute in its commitment to work with the United States and all freedom loving people to combat international terrorism.
In the days and weeks to come, we will consult closely with our Australian allies regarding an effective response to these attacks.
George W. Bush, Press Release - U.S.-Australia United Against Terrorism Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/280228