This sounds like a pretty impressive effort, as reported in the New York Times:
In less than a week, the United States and NATO have pushed more than 17,000 antitank weapons, including Javelin missiles, over the borders of Poland and Romania, unloading them from giant military cargo planes so they can make the trip by land to Kyiv, the Ukrainian capital, and other major cities. So far, Russian forces have been so preoccupied in other parts of the country that they have not targeted the arms supply lines, but few think that can last. . . .
To understand the warp-speed nature of the arms transfers underway now, consider this: A $60 million arms package to Ukraine that the U.S. announced last August was not completed until November, the Pentagon said.
But when the president approved $350 million in military aid on Feb. 26 — nearly six times larger — 70 percent of it was delivered in five days. The speed was considered essential, officials said, because the equipment — including anti-tank weapons — had to make it through western Ukraine before Russian air and ground forces started attacking the shipments. As Russia takes more territory inside the country, it is expected to become more and more difficult to distribute weapons to Ukrainian troops.
Within 48 hours of Mr. Biden approving the transfer of weapons from U.S. military stockpiles on Feb. 26, the first shipments, largely from Germany, were arriving at airfields near Ukraine’s border, officials said.
As the story relates, this is going to get harder to keep doing as Russia takes more of Ukraine. And you’ve got to believe that there will be more direct Russian threats against the conduits in the region for these weapons.