The European Union’s defense ministers are gathering on Wednesday in Stockholm to consider proposals to use the bloc’s budget to order and purchase up to one million shells for Ukraine at an estimated cost of 4 billion euros ($4.2 billion).

That point is to address a production problem. Ukraine is going through shells faster than the West can supply them, but making more shells is expensive. If arms manufacturers are to increase production and build new factories, they want large orders with guaranteed money — and those factories can take two to three years, or more, to come online.

The idea of a huge advance order for shells is one the European Commission president, Ursula von der Leyen, likens to the one used by Europe to secure vaccines early in the Covid-19 pandemic — pooling resources to offer more money up front, as a means of encouraging manufacturers “to invest in new production lines now” for the “standardized products that Ukraine needs desperately.”

Jens Stoltenberg, the NATO secretary general, has told its member nations not to worry too much about reducing their own stocks for now, despite formal NATO requirements, since they could refill them later. But he warned last month that “the waiting time for large-caliber ammunition has increased from 12 to 28 months.”