This is a gold achievement worth 50 gamerscore

This is by far the most time consuming achievement in campaign mode because you must complete all the challenges for the headshots, grenade kills and Intel. this achievement can be done by doing multiple play through of the campaign on various difficulty settings and the kills and headshots will come overtime. as for the grenade kills you can get these quite easily in the mission atlas at the grenade training area. A good thing to know when going for this achievement is that kills and headshots will not stack up over deaths it will only stick once you reach a checkpoint.