To get this, you must beat campaign on any difficulty. The difficulties are Recruit, Regular, Hardened, and Veteran. For this achievement, You can simply beat the campaign on Recruit in 2-3 hours if youre decent. However, I beat it on a combination of Regular and Veteran by bumping up the difficulty through my first playthrough. It is important to mention this has a different feel to it than the first modern warfare and it took me some getting used to. There are many more weapons to choose from, and if you happened to play Rainbow Six Vegas 1&2 these weapons shold be very familiar. The campaign has 16 missions (17 including "No Russian", the one optional mission due to content). For walkthroughs to complete the missions, go to youtube.