When Ultimo rampaged, destroying everything that moved, War Machine called together "Happy" Hogan, Eddie March, Bethany Cabe, Mike O'Brien, and Clayton Wilson. He then proposed that each of them use an old suit of Iron Man armor to help him defeat Ultimo. After the group suited up, they flew out to battle Ultimo, blasting the robot with nearly every weapon in their arsenal.
Ultimo soon fell to the ground, to which Eddie March replied that it was an easy job. To Eddie's surprise, the robot grabbed Eddie and slammed him into the rocky ground. Carl Walker attempted to rescue Eddie, but was blasted by an energy beam himself. War Machine then ordered "Happy" and Bethany to get Eddie and Carl clear of the battle, while he and Michael O'Brien continued to battle Ultimo. "Happy" yelled for Carl to eject from the armor, which he did. Catching him and Eddie, "Happy" and Bethany flew them to safety and quickly rejoined the battle.
The four remaining members of the Iron Legion continued to battle Ultimo until "Happy" and Michael collided with one another, causing "Happy" to dizzily fly about. Ultimo took advantage of the situation and swatted "Happy" to the ground but before Ultimo could crush him, "Happy" managed to fly away. After that close call, War Machine ordered the four to retreat to check on Carl and Eddie. Seeing them hurt, War Machine began to blame himself for their failure in stopping Ultimo from reaching the city of Futura. He then told "Happy" to get Carl and Eddie to the hospital and Michael and Bethany to go to Futura and tell the city to start evacuating. Bethany opted to stay and help War Machine slow Ultimo down, and the two resumed their battle with Ultimo.
The duo didn't fare much better until the timely arrival of Tony Stark, in a brand-new suit of Mark XII armor consisting of updated technology. Iron Man told Bethany to get clear while he battled Ultimo one-on-one. With his new armor, Iron Man managed to take down Ultimo fairly quickly, as War Machine and Bethany returned to view the fallen robot. With the battle over, War Machine punched Iron Man, angry that he let everyone risk their lives only to come in and save the day. War Machine then flew away, while Tony Stark offered Bethany a job.
In Other Media
The Iron Legion appears in the climax of the movie, where they help battle Aldrich Killian and his Extremis soldiers. In the film, the Iron Legion consists of a group of suits Tony built after the Battle of New York, each of which are alternatively controlled by the J.A.R.V.I.S. AI or Tony himself. The suits are all destroyed in the finale after Tony initiates a self-destruct sequence, using the destruction of the Iron Legion as a show of his commitment to Pepper Potts.
The Iron Legion will reappear in this film, as an army of drones used by Tony to help the Avengers in their quest to protect the world.