The Brotherhood of Steel
The Brotherhood of Steel is the primary faction seen throughout the Fallout wasteland and (aside from the Enclave) is the most powerful faction in the storyline. At the beginning they will not let you in the Citadel (their HQ) and are unfriendly, but not hostile towards your character. Their basic armor is..of course “Power Armor” that they ominously wear. They can use a variety of weapons based on their rank: initiate, knight, Paladin, and Sentinel (which is a high ranking commander i.e ‘Sentinel Lyons’). They tend to use assault rifles, laser rifles and mini-guns as their starting weapons but as you progress in level so do they as they gain Gatling lasers, missile launchers, (plasma rifles are added once you have activated “Project Purity” assuming you have downloaded the Broken Steel mission to keep playing. The Citadel has a central courtyard in which you can get permission from Elder Lyons to have the Gunny teach you how to wear power armor. straight ahead is the Brotherhood’s laboratory, to the right is the A section and to the left is the B section. Inside you will find an armory, a doctor and various chances talk to people in the brotherhood (including a chance to score 1000 caps if you get one of the Lyon’s pride to tell you his name in an unmarked quest.)
The Citadel Is Guarded by A Paladin with a mini-gun (he cannot be killed, I’ve tried) as well as several turrets, a sentry bot with a Gatling laser as well as several other knights wielding assault rifles and laser rifles, there are sentries on the wall . and lastly another paladin patroling down with a missile launcher. 
Liberty Prime
the most powerful thing in all of Fallout 3 is Liberty Prime. Throughout the game inoperable due to lack of power supply but as you conveniently destroy the Enclave base its becomes operational and in an overly enthusiastic robotic voice spouts phrases such as “PRIMARY OBJECTIVE… DESTROY ANY AND ALL CHINESE COMMUNISTS AND THE LIBERATION OF ANCHORAGE!” despite the lack of any Chinese in the area it still chooses to pull mini-nukes out of its ass and hurls them at structures even if your right next to it’s target. As you follow along the path of destruction it leaves you are likely to be hit by mortars coming from non-existent cannons. But its primary weapon is what is called the “Liberty Laser” which appears to be rapid fire laser eyes.
(SPOILER ALERT) as you beat the game an start the first mission in Broken Steel it gets about 5 minutes of glory before it suddenly says “WARNING! CHINESE ORBITAL STRIKE DETECTED! RETREAT TO MINIMUM SAFE DISTANCE!” before being blown apart and in a cloud of dust is seen (as the top half) crawling away crying how it died serving democracy. Sadly all that’s left before its head blows off is a shattered torso dragged away by its one remaining arm and a single leg attached to a battered bottom half (the rest of him is scattered around the area).
