Story related, cannot be missed.
After you clear the Blue Line of mutants in Subway Town, Redstone will give you this next quest. You have to assault the Gearhead Vault and find their plutonium inside the bank vault. The enemies here have thick armor (and a few of there own Sentry Bots) so come prepared. Once you make it to the Vault, pickup the plutonium and you'll immediately pickup this achievement.