Take a look:
US Military Sea Lift Command Vessels
These are not officially a part of the US Navy anymore. They are not "USS" vessels, instead, they are "USNS" vessels. Usuallu crewed mostly by Merchant Marines with small US NAvy detachments for communications and operations.
We have a lot of really big ships to move mountains of supplies and have in fact pre-positioned loats of it at places like Diego Garcia, Guam, Saipan, etc.
good to hear