The very first civil heavier-than-air aircraft served as tenders for the airships of the Imperial Postal Service, where a local office would place packages onto an aeroplane which would rendezvous with an airborne airship. The aeroplane would then return to the office (usually gliding, as they would not have enough fuel to perform powered flight in both directions) with packages for the local office. This permitted the airships to function as flying sorting offices. However, in the situations where an airship would have to land (for large quantities of mail, or in order to refuel or repair) the larger local offices would also have a mooring mast. These became the first aerodromes.