Well… what the title says.
From what we know, this is a tested feature for the Stronghold mode – a special type of consumable. A commander will have the possibility of summoning an artillery fire mission to a certain quadrant (the way you click on the map). In case you are wondering, those are 150mm Hummel shells. Each round has 85mm penetration, does 950 damage and has a splash radius of 3,57 meters.