Left No Man Behind

Completed the game on Casual

Nerves Of Steel

Achieved 100% accuracy in any single player mission

My Rifle Is My Best Friend

Completed the game on Medium

Nemesis

Killed Maddox once and for all ("No Loose Ends")

Laugh This Off

In the final duel with Maddox, killed him with the first shot ("No Loose Ends")

Hazardous Materials

Killed three or more enemies by shooting a grenade

Karma Chameleon

Retrieved your weapon without being detected ("Burning Bridges")

Kill With Still

Killed 50 enemies while holding your breath

Say Hello To My Little Friend

Killed 30 enemies using your sidearm

Back To School

Killed all enemy snipers in Sniper Alley without being hit ("Ghosts of Sarajevo")

Hangman's Knot

Killed Major Vladic ("And Justice For All")

Solid Sandman

Killed all enemies in the beach houses without causing an alarm ("Leave No Man Behind")

Operation Archangel

Completed Act 2

Psst, Don't Look Behind You

Killed 15 enemies with a stealth kill

Death's Scythe

Took 50 headshots in single player

Bullets Can't Hurt Me

Completed any act without using medkits

Guardian Angel

Rescued the friendly ("From Out Of Nowhere")

Distance Matters Not

Killed 20 enemies from a distance of 600m or greater

Fisher King

Killed 25 enemies using thermal or night vision goggles

Operation Quarterback

Completed Act 1

Balls Of Steel

Completed any single player mission without using med kits, but taking damage

Worlds Apart

Took a successful shot from a distance of 1 km or greater