National Security Presidential Memorandum: Rebuilding the U.S. Armed Forces, Memorandum for the Secretary of Defense and the Director of the Office of Management and Budget [open pdf - 173KB]
From the "Policy" section: "To pursue peace through strength, it shall be the policy of the United States to rebuild the U.S. Armed Forces." The remainder of the Memorandum addresses "Readiness," "Rebuilding the U.S. Armed Forces," and "General Provisions."
Federal Register: http://www.gpo.gov/fdsys/browse/collection.action?collectionCode=FR
Federal Register (February 1, 2017), v.82 no.20, p.8983-8984