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