Call of Duty: Modern Warfare 2/Armor Piercing

This mission has no time limit, however the enemy will not wait for you to find them. The juggernauts, when activated, will pursue you. There are two ways to fight: wait for them to come to you, or push forward. Pushing is dangerous, as juggernauts may appear around corners, but is required to complete the mission is a shorter amount of time.

To easily complete this mission on any difficulty, have both players keep the starting machine gun (M264?) and equip one of the two available sniper rifles (Barrett .50 cal and an Intervention with a thermal scope) on the tarp on the second platform.

Quickly get your weapons and prepare for the first Juggernaut.

If you wait too long, it may come running down the first flight of stairs. Make your way up into the first building. Using your sniper rifles, position yourselves so you can see the juggernaut coming down the stairs from above, as well as the long platform and the other flight of stairs. From this position, only a small portion of your view will be blocked by a single pillar.
 * Juggernaut #1

Wait for the juggernaut to appear. Immediately pummel it with shots from your sniper rifles. In this position, either player can single-handedly defeat the juggernaut. Because of the positioning, the juggernaut will not attack until it reaches the floor you are on and faces you.

Run up the two flights of stairs and outside. Turn right and run behind the boxes and the wooden fencing on the left. The second juggernaut may or may not spawn immediately at this time, so be prepared.
 * Juggernaut #2

There is an ammo box on the left, with a Grenadier sitting on it. On the right side is an M264?. This is the perfect position to complete the rest of the mission, but you must be prepared to sit tight.

Have player #1, with the Barrett, stand behind the boxes and keep watch for juggernauts coming from behind the fence at the end of the long stretch. Player #2 should be prepared to assist in taking down the juggernauts, as well as setting up defenses.
 * Defensive position for juggernauts #3-15

The player with the thermal scope should pull out their claymores and run up the right side. Plant one to the right of the column, and one at the door to the hostage room from Wetwork. Walk out and to the left where the long stretch is to the next section. Plant a claymore at the corner, then run up to the fence and plant on there. You may trigger the next juggernaut, so prepare to run back through the hostage room to the player standing guard with the Barrett.

Plant a final, fifth, claymore inside of the hostage room, just inside the other door. When ready, run back to player #1 and go prone behind the wooden frame. Alternatively, if player #1 assumes a prone position, player #2 can go behind the object up a short ways and on the left (where the railing zigzags) and stand. In this position, player #2 can see slightly beyond the corner of the fence.

For the rest of the mission (juggernauts 3-15), both players need to be ready to fight at any time. Player #2, if they feel it is necessary, should also be prepared to replace any destroyed claymores. When a juggernaut is coming, the players will be alerted when the claymore by or beyond the fence explodes. If a juggernaut sees a lone claymore, they will shoot and destroy it. It may be best, then, to place the claymore just behind the fence so that it triggers when the juggernaut turns the corner.

Using this strategy, players should only have to fight 1-2 juggernauts at the same time. The downside is that it will take about 15 minutes for them to automatically trigger. If you don't want to spend all of this time scoping the fence, you can remain watching the area like normal. When a juggernaut comes (noted by the music or a blown claymore), simply pause the game and prepare yourselves.

Alternate strategy
At the start, grab the Barret .50 (second player should take Intervention). Follow the above instructions for dealing with the first three juggernauts. These are the only three that are guaranteed to spawn en route to your final objective. Once you have killed the third one, continue moving through the big breach room (from Wetwork) and out onto the helipad where the campaign mission ends. From here, go prone and keep your sights on the door you just exited. This is the only way the juggernauts can reach you.

Reload after each juggernaut until you reach about seven left, then you might have to take them two at a time. If there are two players, communicate and make sure only one is reloading at a time while the other watches the doorway.

Note that if you move to the far corner of the helipad, you can see the lower levels of the oil rig. If you're confident with your sniping, you could drop the juggernauts before they get close. However, they will return fire (although, for the most part, inaccurately). This is only recommended with two players, as you could easily miss one coming right through the doorway.

Quick completion strategy
To quickly complete this mission, you will have to push through each activation area. These areas vary depending on the time that has passed, but there are typically distinct areas where juggernauts re-occur. When assaulting juggernauts, its best to have a combination of a sniper rifle or explosive, and the M240B machine guns that you start with. Sniper rifles and explosives will both heavily damage and stagger them. Remember to flashbang juggernauts to give you enough time to shoot or stab them. Using the knife is not recommended because of the required number of hits and close proximity.

The first juggernaut comes immediately if you push up the stairs. By the time you reach the outside, you will have met it.

The second juggernaut will appear near the first hostage room, or past the fence.

The third juggernaut may appear on the stairs.