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