The army was assembled in FA 510 after Maeglin's betrayal under the leadership of Gothmog. The army appeared to be the most advanced in technology compared to the rest of the Glamhoth. It was made up of Orcs, Trolls, Werewolves, Dragons, and Balrogs. They surrounded the city and besieged it killing nearly all save for the few that followed Tuor and Idril.
In older versions, they used iron machines fueled by "internal fire" as personnel carriers and to destroy fortifications.