The Bigger They Are...

The Bigger They Are... is a PC/Xbox 360 achievement and PS3 trophy earned by killing all 5 Super Mutant Behemoths in the game.

The Behemoths can be found at:
 * GNR, specifically the GNR Building Plaza (Main Quest)
 * West of Jury Street Metro by the old trains
 * Evergreen Mills
 * Capitol Building
 * In between Takoma Park and Takoma Industrial

Once the last Behemoth dies (not necessarily killed by you) you should unlock the achievement/trophy.

Tips

 * To find the GNR Behemoth just follow the main quest without skipping any of it and you'll come across it.
 * The Jury Street Metro Behemoth will spawn if you take the teddy bear from one of the cages inside an overturned train. Wait a bit after and you'll see it start charging at you from over the hills. Note: it is possible that this behemoth will spawn simply by standing next to the cage for 30 seconds or more (Xbox 360 version). Warning: in some cases, if you have bad timing, Crazy Wolfgang and his caravan might be killed by the behemoth or random encounters
 * The Evergreen Mills Behemoth is cage in its own electrified slaver pen so you can kill it from the cliff heads above (The behemoth can escape if the generator by the gate of the cage is destroyed, which can be sniped from an out cropping of the cliffs south of Evergreen Mills marked by a billboard).
 * The easiest way to find a behemoth in the capitol building is to enter through the west entrance.
 * The Takoma Park behemoth is found by heading to the left of a battle between Talon Mercs and Super Mutants to a truck with a merc on top of it (Which has a switch to a Mini-Nuke artillery strike).
 * The Takoma Park artillery strike can be fired numerous times but the switch may break. However, it can be repaired with a high enough repair skill level.
 * It is suggested that you have a Fat Man
 * A Fat Man may take up to 3 shots to kill a behemoth, whilst the Experimental MIRV will kill anything in one shot. Of course, the MIRV is not very practical to kill anything with considering it fires 8 mini nukes at a time, which is a complete waste of ammo when you could just use a normal fatman to shoot it 2-3 times, depending on your big guns skill. But it would be effective.
 * If Fawkes can be moved to a safe location, he can quite quickly kill a Behemoth. (Not always. The Behemoth at GNR easily killed Fawkes.)
 * It is entirely possible that the Capitol Building Behemoth will be killed by a Talon Company Merc-- you find the Behemoth and some other Super Mutats engaged in battle with Talon Mercs, one of which has a Fat Man.

Trivia

 * The name of this quest is derived from the English idiom "The bigger they are, the harder they fall."