Jack Teixeira, the 21-year-old Airman First Class in the Massachusetts Air National Guard who was arrested on Thursday in connection with the intelligence breach, was trained as what the military calls a “Cyber Transport Systems Journeyman.”

The service’s career website says cybertransport systems specialists are responsible for keeping the force’s communication networks running. Airman Teixeira is assigned to the 102nd Intelligence Wing, headquartered on Otis Air National Guard Base on Joint Base Cape Cod in Eastern Massachusetts.

The job mandates that applicants complete what the military calls a single-scope background investigation, which is required before being granted a top-secret security clearance.

It is not clear what security clearances Airman Teixeira might have had, or how he might have gotten access to the materials that were posted online. Those questions are sure to be at the heart of the continuing investigation and any political fallout from the security breach.

When a reporter for The New York Times called the executive offices of the wing, a person identifying himself as Colonel Gordon twice directed any questions to the Department of Justice or the Federal Bureau of Investigation.

Located near the base of Cape Cod in the town of Bourne, a few miles beyond the twin bridges that link the peninsula to the southeastern Massachusetts coast, the base sprawls over thousands of inland acres, surrounded by swaths of dense pine forest. A reporter who drove onto the base late Thursday was stopped at a guard booth and asked to leave the property. A guard referred questions to the Justice Department.

The surrounding area, known as the Upper Cape, is generally viewed as more down-to-earth than the better-known, more upscale resort towns found further to the east. Residents said the number of jobs and employees on the base have declined with the years; several said they had been surprised to learn that someone working there might have been responsible in some way for the leak.

The site has been most often in the news in recent years for providing temporary housing for groups of people in urgent need of shelter. Evacuees displaced from New Orleans by Hurricane Katrina found shelter there in 2005, while last year, a group of migrants flown to Martha’s Vineyard by Florida Gov. Ron DeSantis were later moved to housing on the Bourne base.

On its official website, the wing lists its mission as providing “worldwide precision intelligence and command and control along with trained and experienced airmen for expeditionary combat support and homeland security.”

The wing commander’s biography says he is responsible for 1,260 military and civilian personnel, and their duties include responding to domestic emergencies in Massachusetts while training for wartime missions.

Those missions are given as “intelligence, surveillance and reconnaissance operations, cryptologic intelligence, cyberengineering and installation support, medical and expeditionary combat support.”

A unit at the Otis base also processes intelligence from U-2 spy planes, RQ-4 Global Hawk and MQ-4 Reaper drones and provides support to the National Geospatial-Intelligence Agency. That unit, the 102nd Intelligence, Surveillance and Reconnaissance Group, is a subordinate unit of the 102nd Intelligence Wing.

The 102nd Intelligence Wing publicly lists several job openings for airmen in signals, cryptologic and geospatial intelligence.

The state of Massachusetts has a long history with the National Guard, which was founded there on Dec. 13, 1636, according to an official website which notes that the first Guard aviation unit in Massachusetts was authorized in 1921.

Since the attacks on Sept. 11, 2001, airmen of the Massachusetts Air National Guard have flown air patrols over the East Coast. They have long supported combat operations overseas as well.

The Massachusetts Air National Guard website says that members can choose among 200 different career fields and will “learn leadership skills that today’s employers value.”

“No matter what you’re interested in,” the website says, “there’s a good chance you’ll find it here.”

The Pentagon provided little information about how Airman Teixeira might have gotten access to the material or what security reviews might be underway.

In a statement emailed to reporters in the hours after his arrest, Defense Secretary Lloyd J. Austin III pledged his support to the Justice Department’s investigation and said that he would “continue to review the national security implications” of the unauthorized disclosure of classified material.

Mr. Austin said he would “not hesitate to take any additional measures necessary to safeguard our nation’s secrets,” and that he had directed a review of intelligence access, accountability and control procedures to inform the Pentagon’s efforts to “prevent this kind of incident from happening again.”

Anushka Patil contributed reporting.