Aligned against that plan is a US military that has become increasingly adept at urban warfare during the past 15 years, as well as the people of Mosul themselves.
Reports suggest that opponents of the Islamic State within the city have long been working with the US-Iraqi coalition to provide intelligence – including targeting information – and to engage in anti-Islamic State psychological operations.
This could be crucial, since Islamic State fighters have been in the city for two years. They’ve built up “very elaborate defenses,” Col. John Dorrian, spokesman for US forces in Baghdad, told reporters on the eve of the offensive. “They have fighting positions, they have tunnels.”
The timeline for the liberation of Mosul depends on this intelligence and the extent to which US forces have been able to impart their own urban warfare skills to Iraqi troops.
“We’re good at this stuff,” says retired Col. Peter Mansoor, professor of military history at Ohio State University.
Preparing for Mosul
During recent months, US forces “have clearly tried to bring the Iraqi Army up to those same standards, and I’m sure Iraqi troops are better prepared than when ISIS first entered the country in 2014, but it’ll be a much slower type of fight than what we saw the US Army wage in Fallujah in November, 2004,” adds Professor Mansoor, who served as executive officer to then-Gen. David Petreaus, commander of US forces in Iraq, during the surge of 2007-08.
That said, they have “lots of [US] air power to help them, time is on their side, and they’ll eventually prevail.”
Mosul is the largest and arguably the most important city in the Islamic State’s would-be caliphate. It is the place where the caliphate was declared by Islamic State spiritual head Abu Bakr al-Baghdadi.
“It is the beating heart of Iraqi Sunni nationalism,” says Nicholas Heras, fellow in the Middle East Security Program at the Center for a New American Security.
Going forward, a central question is whether the roughly 3,000 to 5,000 Islamic State forces remaining in the city will choose to stand and fight, particularly in the central districts.
“It could go either way,” Mr. Heras says.
What about a ‘sneak attack’?
Republican presidential candidate Donald Trump has suggested that coalition forces gave up a potentially key advantage when they failed to launch a “sneak attack” in Mosul, lamenting the decision as “stupid.”
Others reject that logic. “Everyone knew Mosul was next,” including the Islamic State, says Mansoor. “Just think back to the spring of 1944. Germans knew the invasion of France was coming. They didn’t know where, or how, but they knew.”
Not keeping the operation secret allowed coalition forces to warn civilians to take shelter, as ABC news reporter Martha Raddatz mentioned while moderating the second presidential debate.
“There are sometimes reasons the military does that,” she said.
“I can’t think of any,” Mr. Trump responded.
“It might be to get civilians out,” she added.
In the days leading up to the offensive, coalition forces dropped pamphlets, hoping to do just that. But it seems clear that the Islamic State is not letting them go.
The result? “It shows we tried,” Mansoor says. “There may be some people who are still trying to leak out.”
What was kept relatively secret was the extent to which the coalition had allies within Mosul itself. That secrecy was crucial, Heras says.
“That, to me, says that one of the areas that most needed to be kept secret and covert was kept secret and covert,” he adds. “It says is that the coalition seems to have done an effective job of holding a number of cards that you could play to undermine ISIS close to the chest.”