Such ships are held in reserve against a time when it may be necessary to call them back into service, and are usually tied up in backwater areas near naval bases or shipyards to speed the reactivation process. They may be modified, 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 — if for nothing else, their bilge pumps need to be run regularly to reduce corrosion of their steel and to prevent the ships from foundering at their moorings.