The related quest becomes available after completing the main steeltown questline and its not missable. After completing the steeltown questline, exit to the worldmap and re enter steeltown 3 times. Next time you exit, you will receive a distress call from the steeltown leader.
Enter steeltown and prepare for a kinda tough fight against Liberty's gangs. People whom you have helped will aid you in battle like Synths and Ghost Gang members. Bot/worker security (depending on who runs Steeltown) will help you too anyway and bot security does the most damage. All allies will use lethal weapons so you should too. Position your vehicle up front and take cover behind it. Winning the battle awards you the achievement.