The new classes in Battlefield 3 merges the 7 classes that were available in Battlefield 2. The four classes in Battlefield 3 are going to be support, engineer, recon, and assault. In Battlefield 2 you had a medic class but it was hardly ever used, mainly because you didn’t get any additional points for doing your task and the weapons were inadequate to defend yourself. The assault class is now the new medic, and it includes a new feature where you can remove your defibrillator and add a grenade launcher attachment instead. So now you are able to customize each class anyway you want. In previous FPS like Black Ops and Bad Company 2, when you see a player that needs to be resurrected, you can go up and revive the player whether they like it or not. In Battlefield 2 the player had a choice whether if they wanted to be revived or not, which gave them a chance to change class; this feature will be brought back in Battlefield 3. Also the defibrillator will have a longer wait time before you can revive someone again, in Bad Company 2 there were too many people being revived left and right which became really annoying.
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