Now, as the war pivots to the east, the numbers and types of weapons supplied by the United States and Europe will again prove critical for Ukraine. Its forces need to quickly rebuild, to replace equipment lost in six weeks of fighting and to supply the reserve units that the Ukrainian military is now trying to put into the field. They also need to prepare for a new sort of war, with the ultimate aim of not only defending cities but also turning out Russian forces.

“So antitank missiles alone are not going to cut it,” said Michael Kofman, research program director in the Russia Studies Program at CNA, a think tank based in Arlington, Va.

Kofman estimated that Ukraine needs “hundreds” of armored combat vehicles, including tanks, and a tremendous amount of ammunition.

Reznikov ticked off a longer list: air defense systems and combat aircraft to protect citizens and Ukrainian troops from missiles and airstrikes; long-range artillery to keep Russian forces at a distance; tanks and armored vehicles to break through Russian defenses and liberate the occupied territories; and anti-ship missiles to beat back the Russian naval siege and unblock ports on the Black Sea.