; 6 U.S.C. 223(a)(7) ). (7) Unmanned aircraft system The term unmanned aircraft system has the meaning given such term in section 44801 of title 49, United States Code. 3. Border wall construction (a) In general (1) Immediate resumption of border wall construction Not later than seven days after the date of the enactment of this section, the Secretary shall resume all activities related to the construction of the border wall along the international border between the United States and Mexico that were underway or being planned for prior to January 20, 2021. (2) Use of funds To carry out this section, the Secretary shall expend all unexpired funds appropriated or explicitly obligated for the construction of the border wall that were appropriated or obligated, as the case may be, for use beginning on October 1, 2019. (3) Use of materials Any unused materials purchased before the date of the enactment of this section for construction of the border wall may be used for activities related to the construction of the border wall in accordance with paragraph (1). (b) Plan to complete tactical infrastructure and technology Not later than 90 days after the date of the enactment of this section and annually thereafter until construction of the border wall has been completed, the Secretary shall submit to the appropriate congressional committees an implementation plan, including annual benchmarks for the construction of 200 miles of such wall and associated cost estimates for satisfying all requirements of the construction of the border wall, including installation and deployment of tactical infrastructure, technology, and other elements as identified by the Department prior to January 20, 2021, through the expenditure of funds appropriated or explicitly obligated, as the case may be, for use, as well as any future funds appropriated or otherwise made available by Congress. (c) Definitions In this section: (1) Appropriate congressional committees The term appropriate congressional committees means the Committee on Homeland