Battle for Mosul: how the military operation will work
There are concerns Mosul may be rigged with explosives and fears Islamic State may have been saving chemical weapons for 'D-Day'.
Monday 17 October 2016 18:15, UK
The first stage of the operation is to encircle Mosul. Joint forces will do this from the north, east and south.
The west will be left open deliberately, allowing Islamic State fighters a route of escape.
It is largely desert in this direction so drones will monitor the terrain and pick off IS fighters as they flee.
Mosul is a big city - it is estimated there could be as many as 1.5 million people left inside.
Senior British commanders estimate Islamic State could have up to 3,000 fighters preparing for the battle. Instead of trying to defend the entire city, they might move into smaller districts.
An intensive intelligence-gathering operation inside the city has been putting together a package of targets for coalition warplanes. Because of the city's density, the risk of civilian casualties is high.
Weather is a factor: the onset of winter will bring cloud cover to the area, making it harder for coalition jets to support forces on the ground. Air support is vital for the confidence of the combined forces.
The Iraqis will lead the fight, but in practice the US will be in control. They have designed the plan. If the Iraqis do something they don't like, the US can withdraw air power.
Some 2,000 Iraqi special forces will be supported by four brigades of the regular Iraqi army, 15,000 Sunni militia, 15,000 Kurdish Peshmerga and a few thousand Shia militia.
Small units and snipers will be sent in first to fight street by street, capturing ground and then handing over to big armies to secure it.
The fear is that Mosul will be rigged with explosives.
In Manjib, a Syrian city that took months to fall, whole neighbourhoods were brought down as forces moved in. That would be extremely dangerous and demoralising.
The other fear is chemical weapons.
There is no doubt Islamic State has the capability, and it is possible the group has been saving the weapons for 'D-Day'.
Radio stations and TV programmes are being set up. They will send positive messages to the residents of Mosul, to reassure the Sunni population in particular and encourage them to lay down weapons.
It is thought some Iraqis have picked up weapons to earn some money and they could be persuaded to turn.
Text messages will be sent to people's phones, keeping them informed of what is planned.
Nobody is putting a time frame on how long it will take to recapture Mosul, but privately there is a hope that significant progress will have been made by the end of the year - not least in Washington, where the Obama administration is counting down its final days.