Plant the C4 in 'Cliffhanger' without alerting or injuring anyone in the blizzard.
This can be done in any difficulty. After you climb the ice and kill both sets of enemies, you and Soap will separate and a blizzard will appear. Take out the gun with the heartbeat sensor and crouch towards the objective. Do not kill or injure anyone and make sure you aren't caught. If you are caught, you can restart from the last check point. Wait for the guard near the objective to move near the car and pass next to him. Do not go inside the building. Move towards the other building on your left, and head towards the edge of it (near the small hill). Soap should mention something about a car but just keep going. There should be one or two dots in your sensor but they can't see you. Ignore Soap when he says there are enemies on the runway, just keep going and plant the C4.
Another way to do this is to follow this video by Mistical:
@callyboi246 best done without killing anybody, let mctavish do the shooting and sneak past the rest. I did this no problems on vet on my ps3, but now im doing it on 360 it wont give me the achiev, Im having same problem as K134U :@ frustrating
got this on vets after only a few checkpoint restarts. very easy, but you have to restart when your partner says "a guard has been alerted", but very casual like so some people may have missed it cuz of that..
Do it on Recruit . You should be okay (Roach kills 2 before they are alerted, so just back out when you suddenly discover those) until Roach says that there are 20+ footmibiles coming up. All I did was wait a bit until they showed up on my rader (hid behind a crate) and when they showed up, I went to my left when you face the fueling station ahead of you. You go around the big storing unit and walk near the fench. You'll reach the fueling station unharmed and unspotted. Got it on my second try.
When I did it on veteran, i didnt alert anyone but I knifed 4 people in buildings. I went back and did it on recruit, it was harder than I expected. Let overwatch take out a few people, he took out two enemies for me. try to stay to the perimeter when possible. Go prone a lot and be patient. laying prone under the jet about 60 m away kept me hidden from the 20+ foot mobiles.
i didnt get this da first time i played thru on normal. i got dis on veteran difficulty second time thru. had 2 restart only a handful of times. its easy as pie. after the ice climbin let him shoot the 4 enemies u first encounter den as u approach da gate jus take ur time n most of the enemies u encounter rite afta da gate he will take out if u stare @ dem long enuff. aside from dat b patient but quik!