; (C) ensure detail design of the vessel is complete before the start of construction; (D) to the extent practicable, use the block-buy contract authority provided under section 1137 of title 14, United States Code; and (E) ensure all icebreaker hulls are science ready and icebreaker hull number four is science capable, as described in the letter report. (2) Definition In this subsection, the term letter report means the National Academies of Sciences, Engineering, and Medicine’s Committee on Polar Icebreaker Cost Assessment letter report entitled Acquisition and Operation of Polar Icebreakers: Fulfilling the Nation’s Needs and dated July 11, 2017. . (b) Technical correction (1) Correction Section 207(a)(6) of the Coast Guard Authorization Act of 2015 ( Public Law 114–120 ) is amended by striking in subsection (d) ( and inserting in subsection (e) ( . (2) Effective date The amendment made by paragraph (1) shall be effective upon the enactment of such Act.