From the Document: "Since 1870, the U.S. military has operated various forms of working capital funds to procure and provide materiel and commercial products and services to its forces. Authorized under Title 10, Section 2208, of the 'United States Code' (U.S.C.), a defense working capital fund (DWCF) is a type of 'revolving fund' that is intended to operate as a self-supporting entity to fund business-like activities (e.g., acquiring parts and supplies, equipment maintenance, transporting personnel, research and development) for the Department of Defense (DOD). DWCF transactions move hundreds of billions of dollars within DOD annually."
CRS In Focus, IF11233
Congressional Research Service: https://crsreports.congress.gov/