Army of Two: The 40th Day

You must complete all checkpoints within the Zoo mission (Chapter 3) on any difficulty. You can play solo with an AI or go at it with a friend in co-op.

You are going be on the streets once again. Your going to encounter some light firepower and some hostages. After you take care of them your going to run into more light firepower and run into your second set of hostages.

After the second set of hostages you will run into a point where you can mock surrender. You will encounter nothing major, a heavy shotty and a few light infantry. Continue after that to the next battle worth talking about, the loading docks. The loading docks will have several foes, just stay to the left side and blast them.

Once they are all dead you will make it outside to the Zoo area. Make your way through two battles to make it to the boss fight. Once the cut scene ends you are going to be placed in the middle of the map. I recommend running/pulling back to the cave area. There will be one light infantry there, take him out and you will have plenty of cover.

He has a grenade launcher, with amazing accuracy and projection. The boss, of course being a super-heavy, can't be hurt with regular means. You are going to have to shot the satchels (bags) on his body. Once all the satchels are gone so will his life.

One last large battle will take place. I always stay near the gates and snipe/takeout everyone from a distance. You will encounter at least two heavies and a ton of light infantry.

Stay on the side of the gate (to the left) and you can take out everything but a few (1 or 2) near the large vehicles that come in.

After that you are done the chapter and your achievement is unlocked! Enjoy!