First lets start with how to see your progress towards this one.
In the main menu of Battlefield BC2, go to the Multiplayer tab and select "Weapons and Gadgets" from the list below that menu point. You will see that there are three kits; Assault, Engineer, Medic, Recon and a general category called "All Kits".
An unlock is a weapon, gadget or specialisation from the kit. In order to get this achievement you have to obtain all that are listed inside one kit. Keep in mind that vehicles count as a kit for this achievement. They have no specific weapons or gadgets. Their specialisations can be found in the "All Kit" category. They constitute the specialisations in the last and second to last row featuring a cog wheel (They don't include the Extended Shotgun Magazine).
To obtain an unlockable you need score. Score can be achieved by playing the class in online matches and gaining kills, assists, badges, securing objectives, etc. The "All Kits" category is an exception as those advance by rank. You rank up by gaining score too. To check your rank, consult the "My stats" menu point under the Multiplayer tab located just below the "Weapons and Gadgets" one.
The easiest way is to get in a vehicle (it was suggested that stationary weapons count as well but I am unable to verify this) and get kills while inside with any means possible. This includes main and secondary weaponry if you should happen to not be in the driver seat. Road kills also count toward this. You will also get assists points if your driver or secondary gunner kills targets.
Below you will find the score necessary to unlock the last item you need for the achievement per kit:
Assault - 47 000
Engineer - 43 000
Medic - 57 000
Recon - 34 000
Vehicle - 10 000
Thanks to
M00SE for posting the list. Although buyers of the special editions get one vehicle item for free which is the one unlocked at 10k, the achievement does not unlock until they hit that mark even though they have everything unlocked at 8k.
The achievement will come as you play normally and I do not think that you need to really go for this one on purpose. It will just take longer if you are not that much into driving vehicles.
Note: Purchasing one of the Shortcut packs will not net you the achievement as commented by
EarthboundX.
Many thanks to
ErichRunner whose comments resolved the matter about what exactly is needed for owners of the special edition to unlock this achievement.
Many thanks for the following comment -
JMJimmy said:Also of note, in Rush style games if you arm a bomb and then jump into a vehicle the points are counted as vehicle points when it blows up (250 pts/bomb). This is especially good if you're playing at slow times on desert maps as you can speed up in a 4-wheeler arm the bomb, jump back on and move to the next target.