The Lewis and Clark class of dry cargo ship is the next class of Combat Logistics Force (CLF) underway replenishment vessels to be constructed for the United States Navy. Lewis and Clark-class ships will replace the existing fifteen Mars- and Sirius-class combat store ships and the s. When operating in concert with a the Lewis and Clarks will also replace s. The first of the planned twelve ships, , was placed in service with the MSC in June 2006, and is being designed for a forty-year service life. The ships will be named for famous American explorers and pioneers.
The primary role of the Lewis and Clarks is to provide logistic lift from supply sources such as friendly ports, or while at sea, from specially equipped merchant ships by consolidation. Lewis and Clarks will transfer cargo (ammunition, food, limited quantities of fuel, repair parts, ship store items, and expendable supplies and material) to station ships and other naval warfare forces. As auxiliary support ships, Lewis and Clarks will directly contribute to the Navy's ability to maintain a forward presence. When operating together with Henry J. Kaiser-class oilers Lewis and Clarks will provide the carrier battle group and/or amphibious readiness group with product lift equivalent to a .
Construction of the lead ship, , was awarded to National Steel and Shipbuilding Company (NASSCO) of San Diego, California, on 18 October 2001. The contract contains options for eleven follow ships. The option for the first follow ship, , was exercised simultaneously with award of Lewis and Clark. The option for an additional ship was exercised in 2002, another one in 2003, two more in 2004 and another two more ships were ordered in 2005. As of 2007, a total of nine ships had been ordered.