By the early 1980s, American-designed 155-millimeter shells were rolling off factory floors in Belgium, Britain, Canada, Denmark, France, Germany, Italy, the Netherlands, Norway and Turkey. And in 2022, Australia, Bosnia, the Czech Republic, Israel, Slovakia, South Korea and Spain are among the contact group nations making them as well.

Does Russia have access to a similar kind of network?

Not really. Although Russia has traditionally been a major arms exporter, it has struggled to resupply its forces in Ukraine. Fewer countries make Soviet-era munitions these days.

In recent months, Russia has purchased and deployed Iranian-made lethal drones in the war, Ukrainian officials say. And Russia is buying millions of artillery shells and rockets from North Korea, according to declassified American intelligence (though North Korea denies this). Whether China, which before the war said its partnership with Russia was unlimited, has sold or given any weapons to Moscow is unclear.

Which allies are providing the most ammunition to Ukraine?

The United States provides about three times as much ammunition to Ukraine as all other members of the contact group combined, Pentagon officials say. But other nations are also making significant contributions.

Mr. LaPlante told reporters this month that the Pentagon would purchase 250,000 additional 155-millimeter shells from several companies around the world, and Douglas R. Bush, the Army’s top acquisition official, said those projectiles were coming from five countries.

Which countries, however, Mr. Bush would not say

John Ismay reported from Washington, and Lara Jakes from Brussels.