US Navy preparing to house 25,000 migrants at remote facilities for up to 6 months: Memo A spokesman said the Defense Department is "conducting prudent planning."

The U.S. Navy is preparing to house as many as 25,000 migrants at remote Navy facilities in California, Arizona, and Alabama, according to a U.S. official with knowledge of an internal Navy document.

The document, prepared for Navy Secretary Richard Spencer by an assistant secretary, appears to have been written in anticipation of the Trump administration requesting the Department of Defense house migrants at U.S. military facilities.

The existence of the memo, which ABC has not seen, was first reported by TIME Magazine.

Earlier this week, the Department of Health and Human Services (HHS) requested that Pentagon be prepared to house up to 20,000 unaccompanied migrant children at U.S. military bases, but it is unclear if the facilities identified by the Navy in the internal memo would meet HHS needs.

The document said the Navy could spend $233 million to construct and operate a facility that could house 25,000 migrants for up to six months. The facilities, which could be constructed as tent cities, are described in the memo as "temporary and austere," the official confirmed.

Although the Navy is preparing to house 25,000 migrants, some of the facilities identified in the document could house up to 47,000. Facilities at former Naval Weapons Station Concord, near San Francisco, and the Marine Corps' Camp Pendleton in Southern California could each house up to 47,000 migrants.

Twenty-five thousand migrants could be located at Navy Outlying Field Wolf in Orange Beach, Alabama and nearby Navy Outlying Field Silverhill. An unknown number of migrants could be held at the Marine Corps Air Station near Yuma, Arizona.

"It would be inappropriate to discuss internal deliberative planning documents," Navy spokesperson Capt. Greg Hicks told ABC News.

Department of Defense spokesperson Lt. Col. Jamie Davis said DoD was "conducting prudent planning" and looking at its installations should the Department of Homeland Security "ask for assistance in housing adult illegal immigrants."

There has not been a request to the Defense Department to house adult migrants, only up to 20,000 unaccompanied migrant children.

Last month, ABC News reported that HHS officials were touring four U.S. military bases to see if they could be used to house migrants in the event that other facilities reached capacity. Those bases did not include any Naval facilities, but Air Force bases in Texas and Arkansas, as well as the Army's Fort Bliss in El Paso, Texas.

While officials have completed their tours of those installations, no final determination has been made as to whether any of those four bases would house migrants.

HHS has used U.S. military facilities to house migrants in the past.

In 2014, the department used bases in Texas, Oklahoma, and California to house 7,000 unaccompanied migrant children after HHS facilities reached capacity.