By Sig Christenson

September 19, 2014 | Updated: September 19, 2014 10:11pm

San Antonio Express-News / File Photo
Workers install surveillance equipment by the entrance to Anzalduas Park in Mission. The deployment of Guard troops began after a surge in immigrants into the Rio Grande Valley

SAN ANTONIO — The Texas National Guard hasn't said how long its border-security mission in the Rio Grande Valley would last, but its operational plan calls for a deployment of up to five months, wrapping up in mid-January.

The Guard's planning document for Operation Strong Safety, marked unclassified but “law enforcement sensitive,” said 920 soldiers could be on duty through Jan. 15.

The plan was leaked to the San Antonio Express-News by a confidential source.

Gov. Rick Perry has said he would deploy up to 1,000 Guard members to the Valley to help stem the illegal crossings of Central Americans who flooded the border this spring and summer.

The Guard is part of a surge of personnel that includes Department of Public Safety troopers and an increase in Border Patrol agents.

Texas Guard officials said Friday the deployment could extend beyond January and last as long as a year.

“The date you are referencing was included in an initial planning document and as such, served as an initial planning factor only,” said Lt. Col. Joanne MacGregor, a Texas Guard spokeswoman. “The actual mission completion date remains unknown at this time, meaning the mission could be longer or shorter in accordance with the governor's direction.”

The blueprint said soldiers would be issued handguns or rifles and given refresher training at Camp Swift in Bastrop.

They received basic Spanish and first aid lessons, as well as how to treat complicated, life-threatening wounds typically seen in combat.

Perry ordered the deployment July 21 after complaining the Obama administration wasn't doing enough to protect the border. The mission started in mid-August.

While Guard members are carrying weapons for self defense, they won't arrest or detain people. Instead, they're to alert the DPS and Border Patrol, a mission called “deter and refer.”

Perry is the nation's only governor to move Guard members to the border at state expense — an estimated $12 million a month. It's costing $6 million a month to support DPS troops who already were on the border when the mission began.

About 120 National Guard soldiers already were on the Southwest border from California to Texas as part of a longtime federal surveillance mission in support of the Border Patrol and U.S. Immigration and Customs Enforcement.

Neither Perry nor the Guard has shared many details about Operation Strong Safety or allowed the media to interview troops on the mission.

However, the blueprint lays out every part of the operation down to such minute details as days when soldiers would be taught basic Spanish and calibrating their weapons during their training, to how they would be paid.

Comparing the document to a book that goes through new editions, MacGregor, the Guard spokeswoman, cautioned it had been updated as new partial or fragmentary orders were issued. She wouldn't describe those changes.

A top mission priority is to find out if groups are preparing attacks in Texas. The second priority is to protect the health and safety of troops.

The command also wants to know if more undocumented immigrants are crossing the border. Those numbers have dropped by more than half from the 4,000 caught in July.

So far, there has been just one incident among the troops — an off-duty soldier was arrested for a misdemeanor offense, but the Guard didn't immediately know the details. He was discharged from the mission.

The Guard asked that the Express-News not disclose the location of specific armories where troops are staying, specific types of equipment being used — including aircraft — or the exact numbers of GIs on duty.

It said hundreds of troops so far have been stationed along the border, but declined to offer a specific figure.

The Guard, in a statement, did not say whether its troops had helped intercept undocumented immigrants, smugglers and criminals. But it also stated there had yet to be a confrontation during the operation.

MacGregor, a veteran helicopter pilot who flew in Iraq six years ago, chafed over the leak of the operational order, saying it was an irresponsible action.

“When one person improperly obtains and distributes a law-enforcement-sensitive document to the media, they violate protocol and Army values, and put soldiers unnecessarily in harm's way,” she said, “and his or her actions do not reflect the professionalism of this organization.”