As Congress continues to battle over immigration legislation, the United States Navy is drawing up plans for detention centers and tent cities designed to hold tens of thousands of migrants.

One project includes creating "temporary and austere" tent cities in abandoned airfields in Alabama, while another proposes extensive detention camps to be built at former army bases in California, according to a military memo obtained by Time magazine.

The internal document stated that the tent cities could house up to 25,000 migrants each, while the camps could hold as many as 47,000 immigrants each. There are four detention sites currently planned for development, and a possibility for more additions in Arizona.

The estimated cost to build and operate a facility that could house 25,000 immigrants for six months is $233 million.

The Navy's chief spokesman, Captain Greg Hicks, told Time he couldn't comment on the plans any further, as it would be "inappropriate to discuss internal deliberative planning documents."

While there is no set construction dates for those plans, it is clear that the military is preparing for the effects of the Trump administration's "zero tolerance" immigration practice, and that the president maintains his stance on securing the border.

The Navy outlined that the first facility could be built in 60 days and hold up to 5,000 immigrants. After the first facility was erected, the military estimated it could build additions to hold 10,000 additional migrants a month.

The memo was leaked just two days after President Donald Trump signed an executive order halting family separations at the border. The action also called on the Department of Defense (DOD) to work with the Department of Homeland Security on the issue of immigration.

"The Secretary of Defense shall take all legally available measures to provide to the Secretary, upon request, any existing facilities available for the housing and care of alien families, and shall construct such facilities if necessary and consistent with law," the order stated.

The DOD is currently planning on housing upward of 20,000 unaccompanied migrant children on military bases across the country starting as soon as July, The Washington Post reported.

Immigrant children, many of whom were separated from their parents under the new "zero tolerance" practice by the Trump administration, walk in single file between tents in their compound next to the Mexican border in Tornillo, Texas, on June 18. Mike Blake/Reuters