Is a collection of naval vessels of all types that are fully equipped for service but are not currently needed, and thus partially or fully decommissioned. A reserve fleet is informally said to be "in mothballs" or "mothballed"; an equivalent expression in unofficial modern U.S. naval usage is "ghost fleet". In earlier times, and especially in British usage, these ships were said to be laid up in ordinary.
Such ships are held in reserve against a time when it may be necessary to call them back into service, and they 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.
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, but like the ships themselves, the stored parts and equipment are prone to fall into disrepair, suffer metal corrosion, and become obsolete.
Information Courtesy of Wikipedia