What are some reasons the Navy decommissions ships?

The Navy decommissions ships to cut costs, to retire obsolete ships and as a result of naval treaties. U.S. Navy ships are given an expected service life and are usually decommissioned when they reach the end of the expected service life.

Some ships have their expected service life extended. For example, the USS Mount Whitney and the USS Blue Ridge had their service time extended to serve another 28 years. The Washington Naval Treaty placed restrictions on certain types of naval ships. The Japanese battleship Mikasa was decommissioned as a result of the treaty. Naval ships are also decommissioned to downsize naval fleets, usually as the result of budget cuts to defense spending.