AVENGERS #21 (1999)

UN troops are being decimated by the cyborg citizens of Slorenia as the Avengers do their best in helping the soldiers advance as Captain America sends Black Panther and Firestar to search for Ultron.  Ultron-16 still holds his "family" prisoner and talks about using Hank Pym's brain patterns to create his "children", which causes Pym to start having a mental breakdown. Ultron notices Black Panther and Firestar approaching and confronts them on his war platform as Firestar signals the other Avengers to their position.  Back at the facility in Virginia, a group of robots take out security and free Alkhema while Justice researchers Ultron's past at the Avengers Mansion.  The Avengers launch attack after attack out Ultron and are unsuccessful until Captain America drives his photonic shield-turned-quarterstaff into Ultron's primary ion channel and Thor summons a powerful lightning strike that hits the same spot and destroys Ultron.  Heading into the tunnels beneath Slorenia, the Avengers encounter Ultron-17, then Ultron-23 followed by Ultron-458 before the ceiling and walls echo with the sounds of what seems like hundreds of Ultrons.