Here is the full list of all 12 Harms Way achievements worth 200 gamerscore. It takes around 1-2 hours to unlock all of the achievements on Xbox 360.
Activate a turret downgrade powerup
Win a game in Single Player
Get the missile launcher for the first time
Deploy mines for the first time
Hit the windshield of a driver
Wreck an opponent as a shooter
Shoot and takeover an enemy turret
Hit the tires of a driver
Join a multiplayer game for the first time
Host a multiplayer game for the first time
Just look at credits
Wreck your vehicle