The National’s correspondent in Erbil, Hugh Naylor, recently did a piece about Arab refugees and Kurdish forces trying to figure out how they can recapture the city of Mosul, sometimes described as the second-biggest in Iraq, with a population perhaps as high as 1.8 million … from the Islamic State fighters who overran it in June.

In Naylor’s story last, week there seemed to be some sense among the sources that it might not be easy to take back Mosul, which at least begins to acknowledge the difficulty of the event, dismissed as not that big a problem about two weeks ago by Iraq’s foreign minister.

In point of fact, professional militaries everywhere in the world view urban warfare as a nightmare, and there is little reason to expect an operation meant to recapture Mosul will be any different.

Let’s assume that the Islamic State is likely to reinforce whatever forces they already have in the city, ahead of a counterattack.

These are not likely to be particularly sophisticated fighters, without much heavy weaponry, but they will have all the benefits that come with defending a city — poor lines of sight for the attackers, the difficulty of deploying superior force in crowded conditions, thousands of strong defensive positions in buildings and rubble and the existence of hundreds of thousands of civilians in the city.

The past century had several examples of urban warfare that was bloody and prolonged and ended with the city being fought over reduced to rubble.

Here are three.

—Stalingrad. The Germans went in holding the upper hand on the Eastern Front. But the Soviets defended the city ferociously, and fighting often was done with one side holding the ground floor and the other the upper floors.

It ended with the German Sixth Army cut off and starving, and surrendering en masse in early 1943.

–Berlin. Same war, but the roles were switched. A remnant of the German army, augmented by children and old men, was holed up in the capital. Despite having a huge advantage in firepower the Soviets needed 12 days to take the city — at a cost of at least 80,000 of their own dead. (Pointedly, Dwight Eisenhower, leader of the American and British forces in Europe, didn’t rush to take Berlin; he let the Soviets do it.)

Again, the city was destroyed, in the process, which the Soviets didn’t mind.

—Hue. This happened during the Vietnam War, in early 1968, after the North Vietnamese and Viet Cong took the city on the opening night of the Tet Offensive.  The South Vietnamese and U.S. army and marines needed more than a month to retake the city. Even with the U.S. at first reluctant to bomb the historic city’s major buildings, it eventually was done and Hue ended as a rock pile.

Mosul seems unlikely to be much different.

It can be retaken. Sure. But the attackers, who are unlikely to be elite units, should expect high casualties, many of them civilians, and should plan on weeks and weeks of house-to-house fighting — unless the Islamic State fighters can be persuaded to leave or surrender or are withdrawn by their leaders, all unlikely outcomes.

And ending with Mosul in ruins.

The same fate could await Tikrit and Fallujah, other significant cities captured by the Islamic State during its “run wild” period in May and June.

Taking back all those places will be hard, but Mosul bulks large in the mind because of its size, and the magnitude of the destruction likely.

“Destroying the city in order to save it” may well be necessary. But any politicians who suggest it will not be supremely difficult … are almost certainly badly wrong.