The president of Ukraine is also expected to participate in a wreath-laying ceremony, having visited Congress earlier in the day.
After his visit to the Pentagon, the Ukrainian president will go on to meet Joe Biden at the White House.
His whirlwind visit to Washington on Thursday is to shore up US support for Ukraine, as Mr Zelensky is facing some Republicans who are now questioning the flow of American dollars that for 19 months has helped keep his troops in the fight against Russian forces.
Lawmakers needed confidence that there was a clear strategy for victory for Ukraine, House foreign affairs chairman Michael McCaul said.
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