Conflict: Denied Ops

Rescuing Bishop comes right at the end of the level so after going through the the level like normal you will find yourself a tank, drive it out into the open area and shoot the enemies around there, at this points two tanks come out, take them both out before either one can do any damage to you. Exit the tank and head over to the structure in the middle of the map and you'll spot Bishop, simply kill all the enemies that ambush you and after a while you'll get some of your men in choppers and tanks showing up and clearing the remaining enemies out for you, the achievement should pop up and the level is complete. 

Rescuing Bishop comes right at the end of the level so after going through the the level like normal you will find yourself a tank, drive it out into the open area and shoot the enemies around there, at this points two tanks come out, take them both out before either one can do any damage to you. Exit the tank and head over to the structure in the middle of the map and you'll spot Bishop, simply kill all the enemies that ambush you and after a while you'll get some of your men in choppers and tanks showing up and clearing the remaining enemies out for you, the achievement should pop up and the level is complete.