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