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