Here is the full list of all 20 Zombie Hunter: D-Day achievements.
Complete the stage D-Day.
Complete the stage D-60.
Complete the stage D-40.
Complete the stage D-20.
Complete the stage D-10.
Achieve Level 10.
Achieve Level 20.
Achieve Level 30.
Achieve Level 40.
Achieve Level 50.
Upgrade firearms 10 times.
Upgrade firearms 20 times.
Upgrade firearms 30 times.
Upgrade firearms 50 times.
Unlock 3 firearms.
Unlock 5 firearms.
Unlock 8 firearms.
Upgrade 4 firearms to MAX level.
Upgrade 7 firearms to MAX level.
Upgrade 10 firearms to MAX level.