Suppression can be delivered by any weapon or group of weapons capable of delivering the required intensity of fire for the required period of suppression. Suppressive fire capabilities vary widely because the suppressive effect area varies widely. For example, a rifle or machine gun bullet may only have a suppressive effect within about one metre of its trajectory, whereas a single artillery shell may suppress a few thousand square metres around its burst. Furthermore, sustained suppression over more than a few minutes may be difficult to achieve with small arms fire for logistic reasons, air delivered suppression is similarly affected by payload limits. In contrast, artillery can suppress an area for an extended period.