1.GNR building.The first behemoth you will face
2.Jury street station.Go directly west untli you find a train station.Look at the cart cages and you will see a teddy bear.Take the teddy bear and the behemoth will appear.
3.Evergreen mills.The behemoth is captured by the raiders and it is unarmed.Have fun killing it.
4.Takoma industrial.Go through the metros to takoma park.You wiil find an artillery and some talon mercs fighting the behemoths. You can easily take the behemoth down with the artillery.