10 U.S.C. § 3131: Availability of appropriations

(a) Funds appropriated to the Department of Defense for research and development remain available for obligation for a period of two consecutive years. (b) Funds appropriated to the Department of Defense for research and development may be used—(1) for the purposes of section 4141 of this title; and (2) for purposes related to research and development for which expenditures are specifically authorized in other appropriations of the Department of Defense.