Here is the full list of all 50 Spec Ops: The Line achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Complete game on "FUBAR" difficulty.
Recover all Intel Items.
Complete any chapter with 60%+ accuracy without dying or reloading a checkpoint.
Play it smart.
Complete game on "Suicide Mission" difficulty.
Choose restraint.
Kill 10 enemies while they use zip lines or are rappelling. (campaign only)
Kill an oryx. (campaign only)
Save a bullet.
Buck the chain of command.
Kill 50 enemies with grenades. (campaign only)
Kill 4 enemies with a shotgun in 10 seconds or less. (campaign only)
Recover 12 Intel Items.
Blow up 10 explosive objects, killing at least one enemy each time. (campaign only)
Kill 50 enemies using only the Attack Command. (campaign only)
Complete three chapters in a row without being killed or reloading a checkpoint.
Kill an enemy just as they are throwing a grenade. (campaign only)
Live and let die.
Live and let live.
Carry on, soldier.
Complete game on "Walk on the Beach" difficulty.
Complete game on "Combat Op" difficulty.
You are relieved.
The end of the line.
Kill 350 enemies with any rifle. (campaign only)
Kill 250 enemies with headshots. (campaign only)
Kill 150 enemies with any heavy weapon. (campaign only)
Choose vengeance.
Get out of here!
Kill 100 enemies with any pistol or SMG. (campaign only)
Hit 10 enemies with your melee attack. (campaign only)
Stun an enemy by dumping sand on their head. (campaign only)
Stand united.
Kick an enemy by vaulting over a cover. (campaign only)
Show mercy.
Kill 75 enemies with any shotgun. (campaign only)
Kill 50 enemies with any sniper rifle. (campaign only)
Kill 3 enemies with a single grenade. (campaign only)
Sprint into cover 10 times while under fire. (campaign only)
Kill an enemy by tagging him with a sticky grenade. (campaign only)
Follow your orders.
Play it loose.
Face the horrors of war.
Kill 5 enemies using blind fire. (campaign only)
Kill an Edged Weapon Expert while he is up to 5 meters away. (campaign only)
Engineer an exit strategy.
We have contact.
Look out below.
What's lost is found.
Recover one Intel Item.