The Support class in Battlefield 3 is equipped with a heavy machine gun capable of delivering great suppressive fire against enemies. The support class also serves a “support” in a literal sense: to resupply ammo to teammates. The support class can either go heavy, with a light machine gun which can be mounted on surfaces with a bipod, or they can go light, with an infantry assault rifle, which provides more mobility and accuracy. The starting weapons for the support class in Battlefield 3 are the M27 for the US, and the RPK for the Russians.
The support class can be extended beyond its main role as a machine gunner and ammo resupplier: the support in Battlefield 3 has many other options, such as the ability to carry C4 explosives, which are useful against enemy vehicles, buildings and much more. Furthermore, the Support can deploy a 60mm mortar, which gives it great long-range capability against enemy vehicles and infantry who have dug themselves in. But always remember that you carry that ammo pack, and to resupply your teammates with it.