The U.S. and its allies are increasingly concerned about Ukraine’s ability to sustain its stocks of Western weaponry on the battlefield. Maintaining weapons is crucial for Kyiv’s fight amid uncertainty over future U.S. military aid, and as Russia increases its arms production.

The task isn’t easy. Ukraine operates a variety of different Western weapons systems whose components aren’t always interchangeable, and engineers said they haven’t received a steady flow of parts from the West. Spares from the U.S. are provided via aid packages, meaning if new funding agreements aren’t reached, the flow of American parts could dry up.