; (B) modification; (C) testing; (D) delivery; (E) sustainment; and (F) program management. 153. Authority to procure additional polar-class icebreakers Section 122 of the National Defense Authorization Act for Fiscal Year 2018 ( Public Law 115–91 ) is amended— (1) in the section heading, by striking Icebreaker vessel and inserting Authorization to procure up to six polar-class icebreakers ; (2) by striking subsections (a) and (b); (3) by inserting before subsection (c) the following new subsection: (a) Authority To procure icebreakers The Secretary of the department in which the Coast Guard is operating may, in consultation with the Secretary of the Navy, enter into a contract or contracts for the procurement of up to six polar-class icebreakers, including— (1) polar-class heavy icebreakers; and (2) polar-class medium icebreakers. ; (4) by redesignating subsections (c) and (d) as subsections (b) and (c), respectively