Section 351(h), relating to hazardous duty pay. (7) Section 352(g), relating to assignment pay or special duty pay. (8) Section 353(i), relating to skill incentive pay or proficiency bonus. (9) Section 355(h), relating to retention incentives for members qualified in critical military skills or assigned to high priority units. (e) Authority to provide temporary increase in rates of basic allowance for housing Section 403(b)(7)(E) of title 37, United States Code, is amended by striking December 31, 2019 and inserting December 31, 2020 . C Travel and Transportation Allowances 621. Extension of pilot program on a Government lodging program Section 914(b) of the Carl Levin and Howard P. Buck McKeon National Defense Authorization Act for Fiscal Year 2015 ( 5 U.S.C. 5911 note) is amended by striking December 31, 2019 and inserting December 31, 2020 . 622. Reinvestment of travel refunds by the Department of Defense (a) Refunds for official travel Subchapter I of chapter 8 of title 37, United States Code, is amended by adding at the end the following new section: 456. Managed travel program refunds (a) Credit of refunds The Secretary of Defense may credit refunds attributable to Department of Defense managed travel programs as a direct result of official travel to such operation and maintenance or research, development, test, and evaluation accounts of the Department as designated by the Secretary that are available for obligation for the fiscal year in which the refund or amount is collected. (b) Use of refunds Refunds credited under subsection (a) may only be used for official travel or operations and efficiency improvements for improved financial management of official travel. (c) Definitions In this section: (1) Managed travel program The term managed travel program includes air, rental car, train, bus, dining, lodging, and travel management, but does not include rebates or refunds attributable to the use of the Government travel card, the Government Purchase Card, or Government travel arranged by Government