Defense Secretary Ashton B. Carter will allow more U.S. troops to be armed while stateside and called for other security measures to be put in place following the attack in Chattanooga, Tenn., that killed five service members.

The decision was outlined in a two-page memo released at the Pentagon on Thursday. Carter in the memo said the ambush, in which an armed gunman opened fire at two military facilities, illustrates the threat posed to the service members in the United States by homegrown violent extremists.

“This incident and the ongoing threat underscore the need for DoD to revise its force protection and security policies, programs, and procedures, particularly for off-installation DoD facilities,” Carter said in the memo, signed Wednesday.

The secretary’s decision comes after a review in which each of the services was directed to submit recommendations on how it would bolster security following the shooting. Carter called for it amid an outcry — and proposed legislation from several congressional lawmakers — to better protect service members working in small, unguarded facilities like the recruiting station and naval reserve center attacked in Tennessee.

Carter’s memo authorizes commanders and civilian directors to “arm qualified DoD personnel for security, law enforcement and counterintelligence duties.” But it adds that those who are not engaged in law enforcement, such as military police, also may be armed “based on the threat and the immediate need to protect DoD assets and lives.”

Carter also called for the Defense Department to improve security at small facilities like recruiting stations through the use of “practical physical security upgrades and procedural improvements,” and to effectively use mass-warning notification systems that can rapidly spread messages through text messages and other means.

The service’s plans must be reviewed, consolidated and presented to Carter by Aug. 21, the memo adds. The document released Thursday does not outline which additional service members might be armed, or what kind of physical security measures might be used.

“These actions will enhance security and force protection and improve the Department’s ability to protect its personnel,” Carter said in the memo. “I know Commanders and other leaders will remain committed to the protection of our dedicated men and women of the all-volunteer force who sacrifice on a daily basis to keep our Nation free.”

Mohammad Youssef Abdulazeez, 24, opened fire at both a recruiting station and a naval reserve center in Chattanooga on July 16. The ambush on the reserve center killed Gunnery Sgt. Thomas Sullivan, 40; Staff Sgt. David Wyatt, 35; Sgt. Carson A. Holmquist; Lance Cpl. Squire D. “Skip” Wells, 21; and Petty Officer 2nd Class Randall Smith, 26. Abdulazeez was killed by responding police officers.

The violence in Chattanooga and the Pentagon’s deliberate response prompted armed civilians to stand guard outside recruiting centers across the country. The Pentagon sought to end that practice last week after an armed civilian in Ohio accidentally discharged a round from a rifle into pavement.

“While we greatly appreciate the outpouring of support for our recruiters from the American public, we ask that individuals not stand guard at recruiting offices as it could adversely impact our mission, and potentially create unintended security risks,” said Pentagon Press Secretary Peter Cook in a statement released Friday. “We continue to partner with and rely on first responders for the safety of the communities where our service members live and work.”

Thomas Gibbons-Neff contributed to this report.