FOR A LONG time, it seemed that a war of attrition between Ukraine and a Russia with five times its population could only end 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 maintain 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 maintain numbers at the front of around 470,000, although it is paying more for them. Production of missiles to strike Ukrainian infrastructure is also surging. But for all the talk about 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.