Such ships are held in reserve against a time when it may be necessary to call them back into service. They are usually tied up in backwater areas near naval bases or shipyards in order to speed the reactivation process. They may be modified for storage during such a period, for instance by having rust-prone areas sealed off or wrapped in plastic or, in the case of sailing warships, the masts removed. While being held in the reserve fleet, ships typically have a
minimal crew (known informally as a skeleton crew) to ensure that they stay in somewhat usable condition. For instance,
bilge pumps need to be run regularly to reduce
corrosion of their steel and to prevent the ships from
foundering at their
moorings. When a ship is placed into reserve status, the various parts and weapon systems that the ship uses are also placed in a storage facility, so that if the warship is reactivated, the proper spare parts and ammunition are available. Like the ships, however, the stored parts and equipment are prone to fall into disrepair, suffer metal corrosion, and become obsolete. ==Principal reserve fleets==