"According to the Feb. 19 Central Command briefing, the assault force might include five Iraqi Army brigades, with three smaller Peshmerga and Iraqi brigades in support. Other reporting suggests that a follow-on gendarmerie force of Mosul policemen would be inserted into cleared areas as a stabilization force.
Under optimal conditions and with smart planning, the planned force of 20,000 to 25,000 soldiers might just be big enough. Perhaps the approach of a credible relieving force will itself cause the Islamic State's grasp on the city to crumble. In a best-case scenario, the latent militant and community networks in Mosul could begin to turn against the Islamic State, sealing off their areas and sitting out the battle. And the Islamic State might overreact and hasten its demise with acts of barbarity that spark a rolling rejection of its presence. Any of these possibilities could be accelerated by coalition airstrikes and U.S.-enabled psychological operations that take control of the cell-phone system and allow direct communications with the public. An attacking force would be well served to selectively seize symbolic locations such as Mosul's airport, the adjacent Ghizlani military complex, and even the Tigris bridges.
But attacking with such a small force represents a dangerous gamble. Iraq's post-Saddam military has never undertaken such an ambitious endeavor as the recapture of Mosul. Unless the Islamic State's determination to hold Mosul is far more fragile than anticipated, an assault force of fewer than half a dozen lightly manned brigades could quickly be ground down by the jihadis. The mooted 25,000 troops might appear to have much more than the traditional three-to-one advantage required to attack, but in reality the sheer number of military tasks faced by such a force would quickly soak up and wear down the liberators. In every area of the sprawling city, the security forces would need to defuse dense patterns of booby traps, clear buildings, screen military-age males, and restore stability and services. And getting back into Mosul may be the easy part." WINEP
The 25,000 number is an illusion. The LOC to the north will have to be outposted every foot of the way. The major towns are Sunni and will be hostile in character to the government force campaigning to the north. These will all have to be heavily garrisoned to keep them in government hands.
The Iraqi Army, the Pesh Merga, the Shias militias and the Sunni Arab tribesmen are all groups sensitive to their own casualties. They will shrink as they see men fall along the way. A number more like 5,000 is more likely by the time they reach Mosul.
Once there they will face the classic combat in cities situation. This kind of fighting requires a lot of skill in doing things like clearing buildings from the tope down, "mouseholing" walls so you don;t have to go out in the street. At the same time the value of coalition air will be reduced because of concern for collateral casualties.
A dangerous gamble indeed; if the new Iraqi Army force is badly damaged, the likelihood of greater Iranian intervention in Iraq will be increased. pl