Oh, you mean getting the first door open to the armory? Well, the Nation Guard Depot is in the Northeastern part of DC, almost right against the edge of the map. Go in there with Laser and plasma weapons, as well as some pulse grenades, as there are TONS of robots inside.
Now that you're in, go right and up the stairs immediatly. Jump of the pipe head and continue through the door, past the cubicals, and through another door. You'll turn a corner and (On Normal Difficulty) you'll find a Robobrain and two turrets. Take care of them and continue down the hallway until you get to a drop down to the lower floor where a Mr. Gusty is waiting. Kill it, and head through the door on the left (You'll know it's the right room because there are two food storage devices and two nuka-cola machines.) Go through the door to the armory.
Walk through here until you get to a desk area with some Combat Helmets, Assault Rifles, and SMGs. Get what you want, and continue through the locker room until you get to the firing range. Kill the three or four robots downrange, grab the loot off of the tables, and go downrange and head right into the offices.
From here, it's pretty striaght forward. When you get to a large room with two large lower areas full of cubicals, your almost there. Destroy the turrets and robots (And explore the area, one cubical has a box full of pulse grenades, and the other has two boxes of pulse grenades), and head up the stairs in the middle high area. Go up the stairs, kill the bots there, and you should find a collapsed floor that makes a ramp up to the next level. Be cautious, as there is a Sentry bot at the top. Once you're at the top, take the door back to the first area.
Now, you're back at the original area, but at a higher location. Flip the switch in front of you, and some flashing lights and a siren should come on. Go to the door with the flashing lights and throw a few pulse grenades in for the Sentry Bot waiting there. Now, flip the switch inside and the floor should open to a door that leads to the armory.
Once down there, flip one more switch and you're inside the armory. There's TONS of stuff in here (2 Combat Armor, 4 Combat Helmet, 4 Combat Knife, 4 Police Batons, 2 Radiation Suits, 4 SMGs, 4 Pulse Mines, 4 Frag Grenades, 4 Frag Mines, 4 Pulse Grenades, 10 Purified Water, 4 Stimpak, 2 Buffout, 3-4 Rad Away, 1 Minigun, 1 Missile Launcher, 10 Missiles, lots of 5mm, 10mm and 5.56mm ammo, and the Small Guns Bobblehead.) straight ahead, there should be a large blast door with a terminal next to it. Access it, input the code (once again, you don't need to memorize it.), and go inside. Inside, there will be a single Glowing One. Kill it, and reap your rewards. The Experimental MIRV, 5 mini nukes, a Nuka Cola Quantum (Under the table), and some other, minor goodies such as a sawn-off shotgun.
Wanna listen to me rant about stuff? I started a blog!
https://theloonybinblog.wordpress.com/