As he winged his way over the American heartland almost 20 years ago, then prime minister John Howard crystallised his thinking on how Australia would join the US response to the September 11 terror attacks.

Howard was visiting Washington DC on September 11, 2001, and saw the smoke billowing from the Pentagon after an airliner hijacked by al-Qaeda terrorists slammed into the Defence Department’s headquarters following the attack on New York’s World Trade Centre.