Given the constraints on military operations, if we seriously expect to contain Islamic State what we are probably facing in Iraq is a decades-long conflict – something the West is clearly not motivated to engage in – particularly when there is little prospect of victory in a conventional sense.

The US typically thinks that a new enemy can be defeated fairly quickly with the right application of military force. The US has a systemic weakness for promoting short-term fixes and not foreseeing long-term consequences. Note Iraq and Afghanistan. When the fix is not quick, the generals, who are under pressure to resolve the situation, assert they can do so if given more resources. This is a slippery slope because history tells us the greater the military commitment, the more domestic pressure there will be for its early termination.

The challenge in both Iraq (and South Vietnam) is (and was) how to enable local forces to do the heavy lifting long-term while we advise and assist and try to avoid suffering Western casualties.

A US and Australian commitment to fighting Islamic State is probably sustainable domestically if we limit it to air strikes, logistic support, and a limited training and advisory commitment on the ground.

We had a suitable model in the early days in South Vietnam, when we deployed a training and advisory cadre comprised of 30 middle ranking officers and senior NCOs, known as the Australian Army Training Team Vietnam, with members serving 12 to 18 month tours of duty. The political mistake was to build up to an unsustainable brigade task force of 7600-plus Australians, and nearly 550,000 American troops, at the height of the war.

The outcome from having a small force deployed to Vietnam would probably have been the same as it was with a large force but we would have avoided having as many casualties. The military comparison with Vietnam is only valid to a certain point because modern military forces have a much better capability to degrade a group like IS than was the case against the North Vietnamese and Viet Cong in South Vietnam in the 1970s.

Special Forces are now a useful and non-controversial addition to any deployment mix. They have developed a great deal in capability since Vietnam and have proved their value in counter insurgency operations. In Afghanistan in 2001, they deployed with mobile Northern Alliance fighters and called in rolling air strikes against concentrations of enemy forces. The Taliban forces soon collapsed and the remnants fled into Pakistan.

The aim of air strikes in Iraq (and possibly Syria) should be to surgically destroy IS's military capability and avoid civilian casualties that will alienate the local population. The US has more than enough air power to do the job but the aim with military coalitions is to get allies involved, which is where our FA-18s are a useful addition.

We might be able to achieve more, more quickly, against IS if we were able to work with Syria and Turkey against IS in Syria but the US will not work with Syria's Assad, and Turkey is materially supporting IS because it sees IS as important to overthrowing Assad and re-establishing Ottoman influence in the Levant.

Iran could be useful for harnessing Shia fighters against the Sunni IS but Iran is another nation that the US is unlikely to approach for assistance. Instead we are looking to reluctant "friendly" regional allies, some of whom see more value in assisting IS than defeating it.

Who then might Australian forces in Iraq assist to best advantage? The Kurds in northern Iraq, including the PKK insurgents, are the best motivated ethnic group to use against IS, which has its main capability in northern Syria and surges into Iraq from northern Syria. In assisting the Kurds we would need to ensure they did not get distracted into conducting operations against Turkey in pursuit of their nationalist desire for a Kurdistan (to take in northern Iraq, south-eastern Turkey and north-western Iran). We obviously do not want to alienate Turkey in the lead-up to the 100th anniversary of Gallipoli next year.

Other aspects of an effective campaign against IS are to try to re-Awaken the Iraqi Sunni resistance movement and cut off IS's funding as far as possible. Much of its funding is said to be coming from Turkey, Saudi Arabia and Qatar, and from sympathetic Muslim populations internationally, but we need to know more about the money flow and how we might be able to interdict it. We also need to stop incoming recruits from swelling the ranks of IS. The CIA estimates IS may now have up to 31,000 fighters, double what it had three months ago.

In sum, to contain IS sustainably, Australia needs to be thinking small-scale (less than what we plan to send) and long-term (more than the PM's "many months") but Australian defence planners will inevitably have to fit in with the impracticalities of America's short-term Middle East strategy.

Clive Williams is a visiting professor at the ANU's Centre for Military and Security Law and an adjunct professor at Macquarie University's Centre for Policing, Intelligence and Counter Terrorism (PICT).