Coaxial machine gun

A coaxial mount is when the gun is mounted besidet the main armament. Coaxial weapons are usually aimed by use of the main gun control. It is usually used to engage infantry or other "soft" targets when the main gun collateral damage would be excessive, or to conserve main gun ammunition.

Battlefield 1942
Coaxial machineguns are mounted on the medium tanks, the Panzer IV and the Sherman. They are most likely an MG34 and an M1919, and are very effective against infantry and light vehicles, although with limited ammo (500 rounds) and a relatively short heat up time.

Battlefield 2
The M240C, PKT, MG3A1 and W-85 all make an appearance as the coaxial-mounted secondary weapons of the M1A2 Abrams, T-90, Leopard 2A6, and Type 98, respectively. They perform similar to their counterparts in Battlefield 1942, as well as identical to one another, although without the limited ammo.

Battlefield: Bad Company 2
Both the M240C and PKT appears as a coaxial variation, they can be used by M1A2 Abrams and T-90.

Battlefield Play4Free
Both the M240C and PKT appears as a coaxial variation, they can be used by M1A2 Abrams and T-90.

Battlefield 3
Both the M240C and PKT are most likely appear as a coaxial variation, they can be used by M1A2 Abrams and T-90.