For a long time it seemed that a war of attrition between Ukraine and a Russia with five times its population could end only one way. But the much-vaunted Russian offensive against Kharkiv in the north that started in May is fizzling out. Its advances elsewhere along the line, especially in the Donbas region, have been both strategically trivial and achieved only at huge cost. The question now is less whether Ukraine can stay in the fight and more how long can Russia keep up its current tempo of operations.

The key issue is not manpower. Russia seems able to go on finding another 25,000 or so soldiers each month to retain around 470,000 men at the front, although it is having to pay more for them. Production of missiles to strike Ukrainian infrastructure is also surging. But for all the talk of Russia having become a war economy, with some 8% of its gdp devoted to military spending, it is able to replace its staggering losses of tanks, armoured infantry vehicles and artillery only by drawing out of storage and refurbishing stocks built up in the Soviet era. Huge though these stocks are, they are not infinite.