The Pentagon is diverting $3.6 billion to build fencing along the southern border, including more than 54 miles of new primary pedestrian fencing, according to a letter the Secretary of Defense sent to the chairman of the House Armed Services Committee.

The letter, which The Daily Beast obtained, details where the new fencing will be built. It does not use the word “wall,” but the White House will likely highlight the construction as part of the president’s effort to keep his signature campaign promise.

Esper’s letter describes the location of over 140 miles of new fencing on the border, some of which replaces older barriers. The letter describes both “primary pedestrian fencing”—fencing right along the border designed to keep people from walking across it—and “secondary fencing”—fencing that is typically farther inland and designed to act as a reinforcement. (Those definitions are according to the Federation for American Immigration Reform, which closely tracks border security and pushes for much stricter enforcement of immigration laws.)

“These projects will deter illegal entry, increase the vanishing time of those illegally crossing the border, and channel migrants to ports of entry,” wrote Defense Sec. Mark Esper in his letter. “They will reduce the demand for DoD personnel and assets at the locations where the barriers are constructed and allow the redeployment of DoD personnel and assets to other high-traffic areas on the border without barriers. In short, these barriers will allow DoD to provide support to DHS more efficiently and effectively. In this respect, the contemplated construction projects are force multipliers.”

The largest chunk of new primary pedestrian fencing is planned to run from a point of entry in Laredo, Texas along the Rio Grande for 52 miles, according to the letter. It will cost almost $1.3 billion.

The letter also details plans for more than 30 miles of new pedestrian fencing in Arizona, replacing vehicle barriers and costing $527 million. It also covers plans to replace more than 23 miles of vehicle barriers in New Mexico with new pedestrian fencing. That project will cost $476 million, according to the letter.

A Pentagon spokesperson did not immediately respond to a request for comment.

Critics say the Trump administration’s plan to redirect funding allocated for military construction projects to border fencing breaks the law. California Attorney General Xavier Becerra has called it an “illegal money grab.” Meanwhile, the president’s critics on the right say his administration is overstating his progress on border security, given that it reportedly hasn’t built any new barriers where none previously existed.