Planetside 2 is a free to play MMOFPS made by Sony Entertainment Online, its been out for a few years but I suggest checking it out because it Free to Play, it has massive battles between Infantry, Vehicles, and Aircraft that can easily have 100 or more people participating, and unlike some many games where the starter weapons are pretty bad the default weapons are pretty powerful and all of the weapons are sidegrades to each other.

The three factions that you can choose from are the TR who use lower damage rapid fire weapons, the NC who use hard hitting low ROF weapons, and the VS whose weapons have low recoil and no bullet drop.

Planetside 2 plays similar to the Battlefield games except on a larger scale but with lower time to kill weapons.

Anyway you can get Planetside 2 here or on Steam for the PC and it is set to be released on PS4 in a bit.