Fission Mailed Achievement
Kill 25 Martyrs by shooting the Bomb Packs on their chests.
Only Mission 2 (right after the opening parachute sequence you can take out 6-7 martyrs) and Mission 3 (halfway through the mission) have martyrs. Shoot 25 in the chest to make the bomb packs explode. This may not be achievable on 1 playthrough because I believe there are less than 25 martyrs.