The army arrives with Rogard outside the Hughes' Residence, and they take Hogarth Hughes, his mother, and Kent Mansley to McCoppin Scrapyard, where Kent confronts the scrapyard owner Dean McCoppin about the Giant. Dean shows them his giant sculpture which is actually the Iron Giant in disguise, but added several metal pieces to fool them. Furious, Rogard calls Kent out for wasting his time and fires him. The army leaves the scrapyard.
Later, Kent Mansley spotted the Giant in Rockwell and the army turns back, now believing Kent. The army began shooting bullets at the Giant which causes it to run with Hogarth, and fly away in the sky. But the Army shot the robot down with a cannon, and when some of the army fired from behind, The Giant goes on a rampage, leaving the army vulnerable and no match for the robot. They border off the town due to the Giant's rampage, but they are unaware that Hogarth brought him back to his senses.
When they are about to open fire, they realize that the Giant is innocent and Rogard orders them to step down. But Mansley orders the USS Nautilus to fire the missile at the Giant. Rogard berates Mansley for causing a doomsday to have in Rockwell, prompting Mansley to attempt to escape Rockwell to save himself, only for the Giant to block his path, allowing the army to arrest Mansley in custody for his crimes and treachery. When the Giant sacrificed himself to save the town from destruction, the army leaves with Rogard. They are later mentioned when they found what's left of the Giant.
The United States Army appears as a guest appearances in Dexter's Laboratory 3rd season episode Smells Like Victory when Dexter is caught in a predicament after the U.S. army invades his lab thinking that there are aliens using it as a base of operations. Not only that, he has to convince the Army that it's his lab, and keep this as a secret for his dad not realize.