Once the Islamic State-controlled city of Mosul falls to Iraqi government forces Australia should bring its troops home, a leading defence analyst says.
Professor Clive Williams says the fall of Mosul should be a line in the sand.
"We should make a point of saying that once Mosul falls, we're out," he says in a lecture at the Australian National University to be delivered on Monday night.
"There's not much to be gained by extending our conventional military involvement from that point onwards."
Three hundred Australian soldiers plus 100 New Zealanders are now operating inside Iraq training members of the Iraqi military for the fight against Islamic State, specifically the battle to retake Mosul.
As well, the 80-member Special Operations Task Group has been advising and mentoring a brigade of the Iraqi Army's elite Counter-Terrorism Service who have been spearheading the assault on Mosul.
Six RAAF F/A-18 Hornet strike bombers have been attacking IS targets in Iraq and Syria, supported by a RAAF KC-30A airborne refuelling aircraft and a Wedgetail airborne warning and control aircraft. All fly from bases in the United Arab Emirates.
The fourth rotation of the training team is now heading into Iraq for their six-month deployment at Taji, north of Baghdad.
Professor Williams said Australian involvement in Iraq in the US-led coalition was mainly to do with the long-standing alliance with America.
The Taji Task Force had already been reduced because many of the soldiers were underemployed.
Islamic State used civilians as human shields and there were not enough acceptable targets for the number of coalition aircraft on stand-by.
"The Iraqis will be pleased if we leave because they don't want us there," Prof Williams says.
"The Americans will make behind-the-scenes overtures for us to stay, but they understand that our main strategic interests are in East Asia."