The U.S. Navy got the first of a new type of support ship in 2013: The Expeditionary Transfer Dock. This was a large tanker-type hull but with the capability to ballast down and transfer heavy items, like landing craft into the sea. Only two were built and they were operated by the Military Sealift Command and civilian-manned. Those two ships, designated T-ESD, are now inactive in reserve.
The T-ESDs were followed by a class of ships with a similar hull design but the addition of a large flight deck. These are designated ESB (Expeditionary Sea Base) and the Navy is building six of the type. The ESBs are commissioned ships and military-manned. Of the three already in service, one is based in Bahrain, one in Crete and one in Saipan. My impression is that the ESBs have been primarily used for basing mine countermeasure helicopters and special operations forces, but they seem to be very versatile. They have only light weapons, so are only suitable for low threat operations.
https://en.wikipedia.org/wiki/Expedi..._Transfer_Dock