During the Cold War, the U.S. government commissioned Tony Stark's father Howard to build a fail-safe weapon to be used if the communists won. Stark created Project Tomorrow, which included two highly-equipped robots, Alpha and Beta units, and a computer guidance system dubbed Mistress (based on the brain patterns of his wife, Maria.) Once the Cold War wound down, the Arsenal units were deemed too dangerous, and were stored away under what would become Avengers Mansion.
Years later, the Beta unit was awakened by accident when the Titanium Man (Boris Bullski) sent a radio transmission to his ally the Unicorn (Milos Masaryk), who was being held in the Mansion at the time. Without any updated programming, this Arsenal robot believed the Avengers to be communists who had taken over New York. Defeating the heroes and the Unicorn, Arsenal was only stopped when Iron Man damaged the robot's circuitry. The Beta unit Arsenal retreated to its hidden chamber below the Mansion, biding its time for another assault. Mistress sent the repaired Beta Unit back to the surface to ascertain the time period. Arsenal battled and captured the Beast (Hank McCoy) and Hawkeye (Clint Barton), then overpowered the rest of the Avengers. Before Arsenal could kill any of the heroes, Iron Man convinced Mistress that the Cold War was over. With her mission obsolete, Mistress shut down. The Arsenal Beta unit apparently destroyed itself as well, but, in actuality, it had gone back into hiding. Months later, a confused and damaged Beta unit re-emerged and sought to re-establish its connection to Mistress. The robot fought the She-Hulk (Jen Walters) and her cousin, the visiting Hulk (Bruce Banner), who shattered it.
Eventually, Senator Zimmer informed Iron Man that there was another Arsenal robot, the Alpha unit, held in stasis below the Mansion. Iron Man was sent to find and dismantle it, but his fellow Avengers unwittingly activated it by interrupting a radio decoding transmission from Zimmer to Iron Man. As with the other unit, the Alpha Arsenal easily withstood the heroes' assault. Iron Man called in Warbird and a team of Homeland Security officers, but they were still no match for the robot. Iron Man finally realized that the Arsenal Alpha unit had only reawakened when his radio frequency was disrupted. The armored Avenger kept Arsenal preoccupied while Warbird found and destroyed the radio jammer that caused its revival. Once again receiving the programmed signal, Arsenal shut down. Homeland Security took command of the situation and dismantled the robot.