ArmA III is a military shooter which focuses on a more realistic approach than contempary first-person shooters. This means that firefights happen from large distances, squad commanders have a lot of commands available to give their soldiers and players can use various cars, tanks and aircraft (although with a less realistic flight model than Bohemia's Take on Helicopters). There are no big differences to Arma II; besides the new underwater simulation they are mostly found in details. Despite being set in 2035, there are no science-fiction elements.
The scenario is in set in Mediterrian Pacific and the backdrop story is about a civil war between Altis and the island Stratis (based on Lemnos). The war parties are NATO, CSAT, AAF (the army of Altis) and FIA (a rebel organization). Both Altis and Stratis are open and are in principle open to explore. However, this is no open world game; it is mission-driven in all playing modes.
The game features various co-op missions in which players (depending on the scenario, up to ten) fight against AI-controlled opponents: in "Escape from Altis" respectively "...Stratis" a squad has to visit and survive checkpoints on the island in order to escape by boat or helictoper; "Tanks" and "Combined Arms" are firefights with, well, tanks respectively infantery combined with vehicles; and "Headhunters" is a hunt against enemy officers. Special are the modes "Defend" (defending an area) and "Seize" (capture AI-controlled points) because players are divided into two teams - while they are allies, it is still possible to fight each other. In this context it is important to mention that the editor is very open, there are many user-created playing modes available and the game has no hard-coded player limit.
The original release, the only singleplayer content are four challenges (shooting courses) and twelve showcase missions which basically serve as tutorials for the game's mechanics, e.g. diving, infiltration, using vehicles, sniping, using drones or various big fights. Three army showcases allow to try out all vehicles and weapons from NATO, SCAT amd AAF. Later Bohemia patched in a single-player campaign in three episodes which is set five years after the separation war between Altis and Stratis: the NATO is ready to leave the area but just then new fighting breaks out:
- Episode 1: Survive - The player takes the role of Corporal Ben Kerry who is one of the remaining soldiers which were cut off. It focuses on infantry and guerilla warfare.
- Episode 2: Adapt
- Episode 3: Win