Army engineers have received permission to start planning and building 57 miles of 5.5m (18ft) high fencing along the US border with Mexico.
The Pentagon is diverting $1bn (£758m) of funding to support the project, which acting defence secretary Patrick Shanahan says is designed to block “drug-smuggling corridors”.
The fencing is going to be erected in Yuma, Arizona and El Paso, Texas – and both areas have recently seen illegal border crossings increase.
Many of those who attempt to cross are asylum-seeking families from Central America.
The Emergency Election Sale is now live! Get 30% to 60% off our most popular products today!