CNN  — 

The military is preparing to send approximately 5,000 more active duty troops to the US-Mexico border, officials said Monday.

The new deployment, dubbed “Operation Faithful Patriot,” is expected to start on November 5 and go until December 15, a US defense official said Monday. Another US official familiar with the plan cautioned that the number of troops could increase or decrease as needs are assessed.

It’s a move aimed at sending a message as a migrant caravan makes its way through Mexico, drawing the ire of President Trump.

But it’s important to note that even though troops are involved, the military isn’t bracing for battle.

Officials emphasize that if the troops carry arms, it will be solely for self-defense. And troops are not expected to come into regular contact with migrants. They will be tasked with providing “mission-enhancing capabilities” along the southwest border, supporting US Customs and Border Protection’s work there.

The caravan is likely weeks away from the US border. And legal restrictions limit what troops can do on US soil.

What isn’t permitted? What can they do? And what questions are we still waiting for administration officials to answer?

Here’s a look:

What they can’t do

For Border Patrol agents, arresting undocumented immigrants and drug trafficking suspects is part of their job description. But National Guard troops will be limited in how much they can do to help.

There’s a law that dates back more than a century known as “posse comitatus” that bars active-duty US troops from domestic law enforcement without authorization. Other laws and regulations have further clarified that troops can’t participate in activities such as making arrests and conducting searches, according to a Congressional Research Service analysis.

So how far can they go? Past presidents haven’t tested these boundaries and therefore courts haven’t weighed in. The Trump administration so far has avoided questions about how exactly it interprets these restrictions, saying lawyers are examining these issues.

Homeland Security Secretary Kirstjen Nielsen told Fox News on Friday that the military has “no intention” of shooting at anyone in the caravan, but she noted that officers of her agency and troops alike have the right to defend themselves.

In past border operations, officials have said National Guard troops can’t:

• Arrest people

• Seize drugs

• Conduct searches

What they can do

Details are still emerging about plans for this deployment. Friday, the Pentagon explained what the troops will provide:

• Planning assistance

• Engineering support with temporary barriers, barricades and fencing

• Aviation support to move US Customs and Border Protection personnel

• Medical teams to triage, treat and prepare for commercial transport of patients

• Command control facilities

• Temporary housing and personal protective equipment for CBP personnel

Unanswered questions

Officials have said this is a separate operation from the National Guard’s efforts to reinforce border security. That mission has approximately 4,000 personnel authorized, but only 2,100 are currently in place, according to the Pentagon.

The plan for “Operation Faithful Patriot” is to send additional active duty troops to Brownsville, Texas; Nogales, Arizona; and near San Diego, California, the defense official said.

But details are still emerging about the operation.

Here’s what we don’t know yet – and what we hope to find out as troops begin arriving at the border:

• Exactly how many troops ultimately will be deployed?

• When will they be armed?

• If so, what criteria will dictate when they can use their weapons?

• How much will this operation cost?

• Who’s paying for it?

CNN’s Barbara Starr, Ryan Browne and Jamie Crawford contributed to this report.