There were plenty of doubters about the Obama-era strategy of training the Iraqi forces, advising them through the battles while supporting them from the air.

But when Mosul finally falls, as Brigadier McAslan of the New Zealand Army says it will "very soon", the slowly but patiently-executed plan, which avoided putting foreign combat troops on the ground - save for some secretive special operations soldiers - will be vindicated.

Brigadier McAslan explains how they've done it in Mosul. It starts with gathering intelligence on the whereabouts of Islamic State commanders and then killing them in precision strikes, mostly from the air.

The Islamic State were regarded as having strong conventional war fighting abilities, partly because they had some of Saddam Hussein's former officers and seasoned foreign leaders among their ranks.

But the relentless strikes have degraded their "command and control" - military jargon for leaders directing their forces - leaving them poorly co-ordinated and in particular unable to fight on several fronts at once.

"They do not get any respite. Daesh has replaced them and as quickly as they replace them, we remove them. We identify where they are and target them," Brigadier McAslan said, using the Arabic name for the group.

"We've had a significant impact on that command and control structure. Daesh are under tremendous pressure and they are not able to react to what the Iraqis are putting in front of them in terms of their manoeuvre on the ground".

The Iraqis, who are being advised by coalition forces in real time as they carry out their operations - including Australian commandos based close to Mosul - have been "synchronising their assault on numerous axes", Brigadier McAslan said.

"Certainly what we are absolutely clear about is that Daesh cannot cope when they have to fight on multiple fronts."

Without sophisticated tactics, the IS fighters have relied heavily on vehicle-borne suicide bombers, mortars and grenade-dropping commercial drones.

The coalition and Iraqi forces have therefore "spent a lot of time and effort" targeting these "critical capabilities" by drawing them out, as the Iraqi ground troops led by the elite counter terrorism and special operations units move in.

"As the Iraqis have advanced, that stimulates the environment, it forces Daesh to make a decision and that exposes them for targeting with our precision coalition fire.

"You see a lot less use of vehicle-borne IEDs [or car bombs], a reduction in the UAVs [or drones] that they were employing, and a reduction in their mortar fire."

In the case of the drones for instance, coalition forces have various systems for disabling the drones, but they have also captured them to track back to their controllers and then hit those sites with precision strikes.

IS still holds about a quarter of Mosul, including parts of the densely-populated west and the old city, which has narrow roads meaning the Iraqi forces will need to move in on foot and fight house-by-house.

Several hundred thousand civilians are reportedly trapped there and are being used as human shields. Brigadier McAslan acknowledges there have been civilian casualties, though he praises the Iraqis' efforts to avoid them.

Brigadier McAslan said that "to all intents and purposes, Mosul is now surrounded".

No more supplies or fighters can get in. Equally the hardcore who remain - reportedly made up mostly of foreigners who are more extreme and cannot melt back into the local population - will make their final stand in western Mosul in a bloody fight to the death.

Asked whether the Iraqis can manage their own security once they've driven IS out, Brigadier McAslan said his forces focussed on their assigned mission of destroying the group but added he was "optimistic" given the strides the local forces have made.

Less than three years ago, he said, IS were "at the gates of Baghdad". Now Iraqi forces are less than a kilometre from Mosul's Great Mosque of al-Nuri where IS leader Abu Bakr al-Baghdadi announced his caliphate.

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