Call of Duty: Modern Warfare 2/Acceptable Losses

Walkthrough
This mission can be done solo on veteran fairly easily but having a second player will help.

You start off facing north in the back alley of a warehouse. Start off by swapping your pistol for a silenced AK-47, as found on the tarp ahead of the starting point. Equip the shotgun with the heartbeat sensor, and run forward to the end of the building and turn right into the snow. Go straight to the other corner of the building and then go straight and diagonally left around the pile of snow and the first jeep.

At the second jeep, duck in front of it, then strafe to the right and quickly kill both enemies (aim at the first one and fire 2-4 times) and reload. Walk over their bodies and turn right; follow the edge of the helicopter and plant the explosives. Back and to the right, along the side of the building you started next to is an enemy walking its perimeter. This enemy can be ignored, but if you successfully knife him in the back you will earn the achievement No Rest For the Wary.

From the helicopter you can choose which objective you want to complete first.

Airplane first
From the helicopter, walk back to where the dead bodies are, then run across the pavement to the cement traffic blocks by the jeep and duck behind them on the right side (facing the airplane). On your heartbeat monitor will be two enemies to the left. They are just beyond the tip of the airplane's wing. Slowly crouch walk forward and strafe to the side when you're ready to kill them; they are lined up just like the first two enemies you killed by the jeep.
 * Enemies 3 and 4

After killing the two lined up guys, walk over their bodies and crouch next to the plane. There is a patrol far to your left, and one should be walking away from you (depending on how long it took you to reach this point). When they reach the far side of their patrol area, sidle along the edge of the plane and then out by its rockets. Plant the explosives and quickly walk back to the bodies of the guys you killed.
 * Planting the second explosives

The enemy jeep should be coming now. To avoid getting getting its attention, run all the way back to the helicopter (the way you came), and then up into the snowbanks. Alternatively, if you know the jeep is very close, you may want to take cover. This is difficult to pull off because the jeep itself acts as an enemy that can trigger the alarm (if you can see the jeep, you probably set off the alarm). Try staying as far away from the road as possible. Think of the road as an enemy - don't get close enough to where it would see you. There is an orange crate behind the airplane on the edge of the snow. You can hide behind it, but be aware of a patrol in the area (it may not be able to see you).
 * Retreat to safety

You should be pretty close to the edge of the first building (between the corner and the first jeep), but up in the hills on the north side of the map by the orange plastic fencing. Stay back a small distance, because there is a patrol that comes through here along the left side.

If no one moving shows up on your heartbeat monitor, then strafe to the wall and walk up to the orange fence. Hop over the side (walking where it is clear may be too close to the enemies inside the building) and walk down to the first box. Don't go into the building yet. Equip your silenced AK-47 and wait for the patrol to appear on the left side (by the open crate that you can walk through). When both are lined up, take them out; with two people, have the other person be near the building and fire at the target in the back.
 * Enemies 5 and 6

Retreat a short distance and prepare to enter the building by equipping your shotgun. The person who goes in first is going to kill both enemies. Turn the corner and kill the guy straight ahead. The second guy should be standing inside the objective's room when you turn to the right (180° from where you entered). Alternatively you can have the other player enter from the back side to kill the guy in the other room immediately. Clear both guys, then walk to the back and plant the explosives. Exit out the back (or return from where you came in and go around the outside) and walk down to the fence on the side of the bunker-like small building.
 * Enemies 7 and 8 and planting the final explosives

This small building is the final threat, but is potentially optional (see next paragraph). It has two entrances that are lined up. One player should go around the back and prepare to strafe out and kill the far right target (sitting in the corner). The other player should go near the front (closest to the third bomb) and kill the target through the glass. If this player misses, the player in the back should kill the target.
 * Enemies 9 and 10 and escape

Alternatively, you can skip these two enemies by crouching and crawling around the corner of the fence behind the building and by the jeep. This is unnerving for some players because of how close you are to the enemy (however, their back is facing you).

When you reach the back of the fence, using either method, walk to the north edge and then walk east to the extraction point. You should see no forces here.

Building first
Now go to the next site on the left. Once you get near the buildings, two enemies will appear, kill them, then go inside and plant the explosives, there may be two enemies inside, one in the main area and one looking through the fridge next to the explosives. if you get spotted, go far to the left. hide behind the crate and use the heartbeat sensor to find out where the enemies are. Once one gets close, kill them. Continue doing this until you are told to be more careful then move on.

The final explosives to plant are fairly hard. Follow the objective indicator using the heartbeat sensor to check for enemies. There will be a few large groups, you can kill them to save yourself the hassle of getting fired upon from all sides or you can sneak past. Near the aircraft there will be two enemies, kill them and quickly plant the explosives then sneak backwards if you are undetected.

Getting to the final checkpoint is easy if you attacked any enemies near the explosives spot in the building. If you didn't, check your heartbeat sensor and pick off the enemies, otherwise sprint to the finish.

Setting off the alarm
If you set off the alarm, you are probably screwed. On lower difficulties survival is more plausible. However, be aware that you will have to kill just about every enemy in the mission. One of the best places to pull this off is near the objective in the building. The small hill to the west of it, with the orange plastic fencing, allows you to peak over the top to kill oncoming forces, but retreat if hurt.

Use the snow to your advantage: if you are taking too many hits, just run away while you heal.