When a ship, especially a naval vessel, is retired from active service, it often spends years in a status known as "mothballed". Ship mothballing allows many critical components of the vessel such as the hull and internal structure to remain stored and preserved in case there is a later need for the ship. Mothballing plays a vital role in defense spending because it is expensive to operate and maintain fully equipped naval vessels, and it takes time to build new ships. Keeping the hull, structure, and vital components in effective storage offers a cost effective compromise in case of crisis.
In a similar vein to the logic behind ammunition mothballing and long term ammunition storage, ship mothballing keeps important investments in major military equipment available in part in case the need arises to refurbish the vessel during a crisis or an opportunity to sell the mothballed ship to an allied nation becomes available. Another common use for mothballed ships is as targets for new bombs and missiles. A hull built to survive battle damage is the ideal test bed for a new weapon designed to inflict said damage. And a vessel so used can, once sunk, be naturally taken over by natural process to form an artificial reef that can become a habitat for marine life.
Ship mothballing itself can provide additional support to storage efforts involving boiler mothballing, turbine mothballing and turbine storage, and even other defense oriented storage efforts. As a ready made internally segmented structures serving little other purpose than remaining inactive and in storage, mothballed ships can themselves hold a variety of equipment that may be useful at a later date.
Another advantage to mothballing ships rather than simply scrapping or selling them at the end of their useful lives is that the equipment unique to their design can be salvaged and used in sister vessels. Ship mothballing can be used to scavenge older hulls that have not stood up well to the test of time and the rigors of naval operations and support hulls that can still function effectively for a few more years. As a historic means of preserving the investment in resources inherent in the physical existence of a naval vessel, ship mothballing will likely continue to offer benefits to future policymakers.