The data spans from August 2023 to January 2024, and the weight corresponds to 1.6 million shells of the type currently used by Russia in its war against Ukraine. The information was provided to the Washington Post by the global security nonprofit Center for Advanced Defense Studies (C4ADS). Analysis of Russian shipment movements during this period suggests the likely origin of the shipments is North Korea. North Korea and Russia have tightened their relationship throughout the course of the war. On June 19, the two signed a mutual defense agreement during the first in decades visit of Russian President Vladimir Putin to North Korea. The pact declared in part, "In case any one of the two sides is put in a state of war by an armed invasion from an individual state or several states, the other side shall provide military and other assistance with all means in its possession without delay.