The troops heading for the border areas of Texas, Arizona and California are a small fraction of the nation's roughly 1.3 million active-duty service members. "Barbed wire used properly can be a lovely sight".
More than 5,000 troops stationed along the U.S. -Mexico border will not receive additional compensation for working in a unsafe environment, known as "danger pay", a Pentagon official said Tuesday.
"We have a problem at the border", he said.
The US military has declined a draft request from the Trump administration to build migrant detention facilities as a part of the Mexican border mission, according to US officials, who spoke on condition of anonymity to Reuters.
From a military standpoint, he said, he asked a number of questions. "Self defense is an inalienable right of an American soldier".
"They want to throw rocks at our military, our military is going to fight back ... we will consider that a firearm" he had said on Thursday. If that number is reached, there will be more troops at the border than in Iraq and Syria.
"Barbed wire looks like it's going to be very effective, too, with soldiers standing in front of it", Trump, who considers the approaching caravans an "invasion" said at a rally in Cleveland on Monday..
In addition, CBP officers have been training with the military soldiers in crowd control measures.
In 2010, Obama ordered the deployment of up to 1,200 National Guard to the US-Mexico border as part of Operation Phalanx.
Trump said last week he plans to build tents to house migrants, who would be held in those facilities while the USA government weighs their asylum request.
There is still no official cost estimate made public for the 45-day mission, but Manning said the Defense Department will "absorb" the costs of the operation.
Active duty USA troops are barred from domestic law enforcement unless there is an emergency, but Trump has repeatedly raised the prospect of having troops enforce the border as he campaigns hard on the dangers of immigration ahead of the midterm elections.
By voicing its opposition, the Pentagon helped ensure that its mission was tailored to providing support only to government personnel on the border.