The Pentagon announced late Monday that it is extending the mission of active duty troops to the Mexico border through September, marking almost a year-long domestic deployment of forces there.

The approximately 4,500 active duty and National Guard forces now on the border were first sent there in late October 2018 to meet a request from President Donald Trump and the Department of Homeland Security to secure border entry points from thousands of immigrants traveling north through Mexico to seek asylum in the U.S. Several units have rotated in and out during that time, and have been tasked to lay concertina wire, barriers and help assist border patrol agents at points in Texas, Arizona and California.

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The mission for those troops extending through September will also slightly change to add more surveillance, but some will still be laying wire, DoD said.

“In response to the December 27, 2018 request from the Department of Homeland Security (DHS), Acting Secretary of Defense Pat Shanahan approved Department of Defense assistance to DHS through Sept. 30, 2019," the Pentagon said in a statement. "DoD is transitioning its support at the southwestern border from hardening ports of entry to mobile surveillance and detection, as well as concertina wire emplacement between ports of entry. DoD will continue to provide aviation support.”