Worms Forts: Under Siege is a turn-based strategy game where 2 – 4 people battle it out with a team of 4 worms. Each player takes timed turns using weapons and forts to cause damage, punch, and blow up the opponent's worms.
The ability to construct buildings has been added to aid in the fight. Buildings such as hospitals can resurrect dead worms, science labs increase firepower, strongholds protect operations, towers deploy weapons from their tops, keeps, castles, and citadels base operations, weapon factories produce multiple weapons, and Wonders must be destroyed or knocked down by opponents within two turns.
Weapons like mini guns, bazookas, rocket launchers, earthquakes, and homing pigeons are available. New weapons have also been added to destroy buildings like trebuchets, fridge launchers, nuclear strikes, and the Trojan Donkey. Some weapons can be steered to a desired location or exploded early.
Different crates will fall from the sky or teleport onto the playing field. Crates contain more powerful weapons, health increases, instant utilities, and collectible utilities like freeze, parachute, jet pack, and repair.
Single play allows for a quick game, tutorial, campaign, trials (death match against the CPU), and viewing gallery. The viewing gallery allows players to unlock movies, view completed content, check credits, and look through Fortapedia.
Multiplayer offers various options such as selecting pre-set weapons and game options, choosing landscapes like Roman, Egyptian, Samurai, and Old World, playing with or against the CPU, and adjusting game settings for a match against other people.