13 November 2025

Guns and Ammo: The Ukraine War and NATO’s Ammunition Interoperability Problem

Eric Johnson

If the war in Ukraine has reinforced one truism of modern warfare, it is that artillery remains the king of battle. Its central role in Ukrainian combat operations has been sustained by the commitment of Ukraine’s international supporters. The extensive provision of artillery shells from the United States and other NATO members led to serious concerns about the depth of ammunition stockpiles and shell manufacturing capacity in both the United States and Europe. A production surge has at least partly mitigated concerns this year, but there remains a separate issue that has received far less public attention and yet is a critical one for NATO: ammunition interoperability.

Interoperability is a central tenet of NATO, and the key to interoperability is standardization. The alliance’s method of choice for achieving this is a set of standardization agreements, or STANAGs. Moreover, in 2009, the United States and four other major NATO members—France, Germany, Italy, and the United Kingdom, signed the Joint Ballistics Memorandum of Understanding (JBMoU), intended to “maximize the potential for the achievement of Interchangeability of the Participants’ 155MM Weapon and Ammunition Systems.” The war in Ukraine, however, has been a unique test of NATO 155-millimeter ammunition compatibility in a way that was not foreseen when STANAGS and the JBMoU were written. Instead of a national army using a supply of ammunition from another alliance nation in an emergency situation, Ukraine is continuously operating a vast array of howitzers and ammunition from across (and beyond) NATO within its own single national army. And Ukraine’s experience has made clear that NATO and JBMoU 155-millimeter howitzers and munitions are not truly interoperable. While they are physically compatible, in the sense that they will safely fire with approved shell, propellant, and fuze combinations, they are not truly technically interoperable until a howitzer battery can achieve accurate first-round effects with munitions from another nation or nations.

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