Ukraine is running out of ammo. The West doesn’t have enough.

As trench warfare has taken over the conflict’s front lines, Kyiv’s and Moscow’s forces have come to lean heavily on old-school artillery — launching round after round of unguided explosives at the enemy. But both sides are now running low ahead of impending offensives, global stockpiles are dwindling, and ramping up will take years.

In this part-explainer, part-investigative mini-documentary — the third episode of our new series The Agenda — Semafor takes a hard look at the state of the U.S. defense industry to answer why supplying Ukraine with the ammunition it...