Bought your first helicopter
Bought all helicopters
Saved the first survivor
Escorted the first convoy
Defeated the first boss
Transported a supply to your base
Defended the first camp
Hired your first shooter
Upgraded a shooter
Veteran shooter acquired
Upgraded a helicopter
Owned a fully upgraded helicopter
Completed the normal difficulty
Completed the hard difficulty
Completed the epic difficulty
Defeated 100 zombies
Defeated 500 zombies
Defeated 1000 zombies
Collected a special paint job
Repainted a helicopter