10 U.S.C. § 191

1. (a)Whenever the Secretary of Defense determines such action would be more effective, economical, or efficient, the Secretary may provide for the performance of a supply or service activity that is common to more than one military department by a single agency of the Department of Defense.
2. (b)Any agency of the Department of Defense established under subsection (a) (or under the second sentence of section 125(d) of this title (as in effect before October 1, 1986)) for the performance of a supply or service activity referred to in such subsection shall be designated as a Defense Agency or a Department of Defense Field Activity.