This is very noob friendly, and most experienced modders could probably figure this out but I figured I'd post anyway.
This will unlock:
Military Police:
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CQB:
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Security (Chest):
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Requirements
Halo: Reach
Atleast 2 Of These Would Help: Halo 3, Halo Wars, Halo 3: ODST
USB Flash Drive / Hard Drive Transfer Cable

First, download this.
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Extract the folder to your Desktop.

1.) Turn on your xbox 360. On the dashboard, go to "My Xbox". If you have a Hard Drive Transfer Cable, skip to step 2. If you're using a USB flash drive, continue reading. Scroll all the way to the right and choose "System Settings". Alternatively, hit the guide button, scroll right to settings, choose system settings. Then, choose "Memory". Choose "Hard Drive" and then "Gamer Profiles". Find the account you would like to receive the armor, and move it to the USB Flash Drive you should have plugged in.
2.) Plug your USB device into your computer (either a USB Flash Drive or a USB Transfer Cable) and open "Modio" (program included in download link). In Modio, click the top left button and scroll down to "Open a Device". Click on it, and it should bring up another window. In this new window, click "File > Open a Device". If everything is plugged in properly to your computer, you should now see folders to the left. On a hard drive, you will see "Partition 1, 2, and 3". On a flash drive, you should just see a folder saying "User Content (Examples Here). Whichever you're using, find your account. If your Modio is updated, it should say your GamerTag in parenthesis next to the code for your GamerTag. For example, it could say "E0000314FA661947 (Enkrept)" if Enkrept was your GamerTag. Repeatedly click the small plus signs next to the folders until you cant go any further and you see the code and your GamerTag again. Now, drag and drop this "E0000314FA661947" (it should look similar but not exactly) onto your desktop. Minimize Modio, and go into your folder you downloaded and open "Le Fluffie".
3.) Here is where having Halo 3, Halo 3: ODST, and Halo Wars would help. If you have them, skip to step 4. If not, continue reading. You now need to add the GPDs of the games to your account. In Le Fluffie, choose "File > Open a File". Find your profile. This will be your code of numbers and letters that you drag and dropped earlier. In my case, E0000314FA661947. Yours should look something like that. Go to "Add Games to the "Profile" tab, and click "Add Games to Profile". A new window should come up. Now, click "File > Add a File" and navigate to your GPDs. Whichever games you don't have are the games you should be adding. For each game you added, you need to highlight it in your games list and click the "Achievements" tab. Click "Save to Profile Save Dash GPD to Profile" (it is all one button).
4.) Click "Unlock ALL" on the right side in the middle of the window. Now, click "Save Account" and exit Le Fluffie. Re-open Modio (it should be minimized) and drag and drop your profile (E0000314FA661947 similar) to the Modio window. It should pop up with your GamerTag and some other information. Click "Rehash and Resign". Then, find the window you used to Open your Device (or re-open it by and drag and drop the E0000314FA661947 similar file (your profile) into the folder "Content" (Gamesaves, Profiles, etc.). Unplug your device and plug it back into the Xbox 360.
5.) Start up Halo: Reach. Hit start, and go to "Halo Waypoint". Say yes when it asks if you're sure, and if you haven't downloaded it yet, wait a few minutes. Then, in the Halo Waypoint Menu, go to "Career". There you go, after a loading sequence, you will have the armor. Start Halo Reach and enjoy! I'll try to make a video tutorial soon. I have the resources but not the time atm.

*This tutorial was made by TallMods. Completely, with no copying or pasting. 100% Original and typed.*