U.S. Marines will begin reinforcing ports of entry at the southwest border beginning Thursday. The move is in advance of a migrant caravan traveling from Central America to the United States, according to a Northern Command spokeswoman.

They will begin “obstacle emplacement” at the ports of entry Thursday, according to Air Force Capt. Lauren Hill.

More than 1,000 Marines from Camp Pendleton were activated last Friday as part of the U.S. military’s mission to help the Department of Homeland Security (DHS) and Customs and Border Protection (CBP). They are assigned to the Special-Purpose Marine Air-Ground Task Force 7, 1 Marine Expeditionary Force.

As of last Friday, they had not left their base. It is not clear yet how many of the Marines have deployed yet.

The Marines will be part of the more than 7,000 active duty troops who will be deployed to the border. About 2,800 will be deployed in Texas, 1,500 in Arizona, and 1,300 in California, according to the Defense Department. The preponderance of the troops are soldiers.

Troops are not expected to come into direct contact with migrants, but will assist CBP agents with transportation, logistics, medical support, and engineering support.

Defense leaders are looking at the deployments as an opportunity for troops to train.

“They are supporting DHS and Customs and Border Protection. If you look at the mix of forces going…it’s logistics, and aviation, and engineers,” Army Secretary Mark Esper said Thursday at the American Enterprise Institute.

“They are getting training out of that, they are deploying, they are putting their equipment on trains and what not, or convoying, and they are deploying to a location and they are offloading, and in many cases these troops are performing the missions that they were designed to perform,” he said.