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.
Kill 4 enemies with a shotgun in 10 seconds or less. (campaign only)
Recover all Intel Items.
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.
Play it loose.
Complete game on "FUBAR" difficulty.
You are relieved.
Choose vengeance.
Save a bullet.
Kill an oryx. (campaign only)
Kill an Edged Weapon Expert while he is up to 5 meters away. (campaign only)
Kill 50 enemies using only the Attack Command. (campaign only)
Buck the chain of command.
Play it smart.
Kill 75 enemies with any shotgun. (campaign only)
Hit 10 enemies with your melee attack. (campaign only)
Kill an enemy by tagging him with a sticky grenade. (campaign only)
Kick an enemy by vaulting over a cover. (campaign only)
Kill 10 enemies while they use zip lines or are rappelling. (campaign only)
Kill 50 enemies with any sniper rifle. (campaign only)
Kill 50 enemies with grenades. (campaign only)
Sprint into cover 10 times while under fire. (campaign only)
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.
Blow up 10 explosive objects, killing at least one enemy each time. (campaign only)
Choose restraint.
Get out of here!
Kill 150 enemies with any heavy weapon. (campaign only)
Recover 12 Intel Items.
Stun an enemy by dumping sand on their head. (campaign only)
Stand united.
Show mercy.
Kill 100 enemies with any pistol or SMG. (campaign only)
Kill 250 enemies with headshots. (campaign only)
Kill 350 enemies with any rifle. (campaign only)
Follow your orders.
Face the horrors of war.
Engineer an exit strategy.
Kill 3 enemies with a single grenade. (campaign only)
Kill 5 enemies using blind fire. (campaign only)
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.