Six of the 12 ships are Maritime Prepositioning Ships -- MV lst Lt. Jack Lummus, SS Maj. Stephen W. Pless, MV Cpl. Louis J. Hauge Jr., MV Pfc. James Anderson Jr., MV 1st Lt. Alex Bonnyman and USNS 1st Lt. Harry L. Martin. These ships, part of Maritime Prepositioning Ships Squadron Three, are collectively laden with enough equipment and supplies to support 15,000 Marines for 30 days. In addition to expeditionary Marine Corps combat equipment, the ships carry food, fuel, medical supplies, construction and road building equipment, electrical power generating equipment, airfield matting and a Navy field hospital.Info on the Amphibious Bulk Liquid Transfer System here.
The squadron also has 43 Reverse Osmosis Water Purification Units, each of which is capable of producing 600 gallons of potable water per hour from sea water. Five of the ships are also capable of making 25,000 gallons of fresh water a day using the ships' evaporators. The ships can pump water from ship to shore from up to two miles away using an Amphibious Bulk Liquid Transfer System of floating hoses.
See the post below here for more info on the MPSRON ships.