Future ships listed are those that are in the planning stages, or are currently under construction, from having the keel laid to fitting out and final sea trials.
One of these, USS Constitution, a three-masted tall ship, is one of the original six frigates of the United States Navy.
She is the oldest naval vessel afloat, and still retains her commission (and hence is listed here), as a special commemoration for that ship alone.
Note A Submarine and special warfare support vessel A Submarine and Special Warfare Support Vessel Ready Reserve Force ships are maintained by the United States Maritime Administration and are part of the United States Navy ship inventory.
Note: Ships listed here may be referred to as "pre-commissioning unit" or "PCU" in various sources including US Navy webpages.