An aircraft comprises a weapons bay, the weapons bay comprising a cavity having an opening through which stores may be deployed, and a door assembly for exposing/closing the opening of the cavity. A first store is held in the cavity via a launcher and a first structure is disposed inside the cavity, for controlling the aero-acoustic environment. The first structure for controlling the aero-acoustic environment is removeably mounted in the weapons bay, such that if the first store is exchanged for a second, different, store, the structure for controlling the aero-acoustic environment may be unmounted from the weapons bay and removed, to be exchanged for a second, different, structure for controlling the aero-acoustic environment.