The Ex-wife is a weapon created by Justin Hammer that was put into war machine and was supposed to be able to wreck any bunker in one shot. When Iron Man Mark VI and War Machine Mark I were fighting Whiplash, Rhody as his first move put out the Ex-Wife as a weapon to win the battle with. Instead of winning the battle, it just bounced off of Whiplash's armor and did nothing. This supports the fact that Justin Hammer can't make anything good, according to Tony.
Iron Man 2 Edit
After James Rhodes stole the Mark II armor from Tony during his birthday party, he brought it to the government and it was upgraded to have more weapons and weapon holders. Justin Hammer showcased several guns and while seeing Rhody's indifferent face, he kept getting better. The last weapon that Hammer showed was the Ex-Wife, which was supposed to be the ultimate weapon. He said it could bust any bunker and the bunker under the bunker you just busted.
Battle with Whiplash Edit
After Tony and Rhody beat the Hammer drones, Whiplash came to the fight and the two sides got ready, to start and hopefully end the battle, Rhody sent the Ex-Wife out. It did nothing and the battle started.