When news broke recently that Texas Gov. Greg Abbott had ordered his State Guard to monitor the controversial military exercise Jade Helm 15 this summer, confusion reigned. Many thought incorrectly that the Texas National Guard would be called in to shadow the operation, whose existence has spawned a number of conspiracy theories.

The Army National Guard and Air National Guard won’t be involved. Rather, the State Guard is a separate state-sponsored militia that also falls under the command of the governor and Maj. Gen. John F. Nichols, the adjutant general in Texas. The key difference between the State Guard and the National Guard: the former cannot be activated for a federal mission.

The attention on the Texas State Guard highlights an often overlooked fact: 23 states and territories operate state defense forces (SDF). Their roles and missions range, but they most often augment the National Guard in times of disaster without requiring the same level of experience, training and physical fitness. They were authorized by Congress in their present form in 1955, and are established through state laws. Many former and retired members of the military volunteer. Some states have members in their 70s.

About 14,000 men and women volunteer for state defense forces, a Defense Department Inspector General report released last year said. It mapped which states and territories have them (they’re shaded):

The report found that the relationship between the Pentagon and these defense forces is “not properly defined.” State defense forces are often not able to fully participate in state missions when required to work alongside the active-duty military or National Guard, the IG noted. Most states limit their defense forces to emergency response, operations center management and ceremonial activities. Others allow them to use facilities and equipment owned by the National Guard, but only if it has been mobilized.

The inspector general received responses from the adjutant generals who oversee the National Guard and state defense forces in 18 states. Notably, only 13 said they considered the state defense force members to be soldiers, and eight said they considered them to be “lawful belligerents,” meaning they have legal protections in any fighting. Only four adjutant generals said the defense forces in their states were authorized to use weapons while on duty.

“The combined responses of State Adjutant Generals and SDF Commanding Generals shows that almost all of the missions assigned to SDF were non-military in nature,” the IG found. “Missions described included support to civilian emergency management, small-scale search and rescue, and other unarmed operations relating to homeland security.”

They have been involved in some high-profile missions. Notably, New York and New Jersey activated their defense forces after the terrorist attacks on Sept. 11, 2001, offering more manpower and medical expertise as authorities sought to save victims trapped in the rubble of the World Trade Center and bolster security elsewhere.

An estimated 2,274 state defense force members from eight states also were involved in recovery efforts after Hurricane Katrina devastated parts of Louisiana and Mississippi 10 years ago. Some assisted directly, while others filled in for National Guard units that had been activated, the IG noted. More recently, the New York Guard was involved in relief efforts after Hurricane Sandy ripped through the state in fall 2012.

The Army says the size and scope of Jade Helm 15, a Special Operations exercise that begins in July, set it apart from other training exercises. Also setting it apart: The widespread conspiracy theories that the U.S. is preparing to hatch martial law. The Post's Dan Lamothe explains. (Tom LeGro/The Washington Post)

In Texas, the State Guard has headquarters at Camp Mabry, a military installation in the state capital of Austin that also has headquarters for the National Guard. It has about 2,000 members, and focuses primarily on emergency response, according to a fact sheet. They train at least one day per month and attend a four-day annual training exercise. A State Guard website said members may be eligible for a daily stipend during training and state emergencies, and offered free licenses to hunt, fish and carry a concealed handgun.

It’s unclear what, exactly, the Guard will be doing in Texas during Jade Helm. Abbott’s April 28 letter ordering the State Guard to monitor the operation said the governor wanted “regular updates on the progress and safety” of the exercise and for State Guard members to “facilitate communications between my office and commanders of the Operation to ensure that adequate measures are in place to protect Texans,” but made no mention of how many Guard members that could require.

Abbott has been criticized for involving the State Guard, including by former Texas Gov. Rick Perry, a fellow Republican. But Abbott has defended the decision, saying it will help communication.

Abbott added that there was “frankly an overreaction” to his decision to use the State Guard to monitor the operation.

“I think that by gathering and disseminating information, it will allay concerns that people have about what’s going on,” he said.