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After a gunman killed four Marines and a sailor at a Navy Reserve Center in Chattanooga last month, the Navy plans to station armed guards at all of its reserve centers across the country, NBC News has learned.

An email sent to Naval Reservists nine days after the attack, and obtained by NBC News, says “VOLUNTEERS NEEDED IMMEDIATELY!” to provide 45 days of “armed sentry watchstander duty” at 53 “NOSCs,” or Navy Reserve Centers, beginning Aug. 17, and also asks for volunteers to provide a full year of armed sentry duty at 70 reserve centers starting Oct. 17.

The Navy confirmed to NBC News that it plans to station armed personnel at all 70 reserve centers that are not located on military bases. The guards would be reservists called to active duty on an all-volunteer basis.

The Navy is also weighing providing armed protection at its recruiting centers, but has not yet authorized armed guards, says a U.S. Navy official.

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“It is being considered along with the rest of the full spectrum of force protection measures,” said the official. “Many additional measures are being considered.”

Before Mohammad Youssuf Abdulazeez killed five people at the Chattanooga reserve center on July 16, he drove past a nearby military recruiting center and fired as many as 30 shots, wounding one Marine. Since the attack, armed civilians have stationed themselves outside some of the nation’s more than 1,000 off-base military recruiting centers to offer protection.

The head of the Marine Corps recruiting command, Lt. Gen. Mark Brilakis, sent a memo advising Marine recruiters not to support the armed citizens and to call local law enforcement if they appeared outside recruiting stations. He said their presence, “while well intentioned, will be counterproductive to our recruiting operations.”

To date, the Navy is the only service that has taken steps to place its own armed guards at off-base facilities. On July 30, two weeks after the Chattanooga shooting, and five days after the Navy email to reservists asking for armed guard volunteers, Defense Secretary Ash Carter issued a memo calling for more service personnel to be armed, particularly at off-site installations, including recruiting centers.

“[The Chattanooga] incident and the ongoing threat underscore the need for DoD [the Defense Department] to revise its force protection and security policies, programs, and procedures, particularly for off-installation DoD facilities,” Carter wrote in the memo.

Carter also called for “practical physical security upgrades and procedural improvements” at facilities, including recruitment centers.

The Pentagon has traditionally limited the presence of weapons in public settings, but allows personnel to be armed in specific circumstances. In its most recent directive, issued April 2011, it said “qualified personnel” could be armed “when required for assigned duties and there is reasonable expectation that DoD installations, property, or personnel lives … will be jeopardized if personnel are not armed.”

The July 25 Navy email to reservists asking for armed guards tells potential volunteers that “there is a strong likelihood that your duty can be performed at your local NOSC is your NOSC is not located at a base/installation. Volunteers must be either MA (master-at-arms) ‘A’ school graduates or have completed the Security Reaction Force – Basic (SFRB) course” and be qualified to fire a 9 millimeter weapon.

NOSC stands for Naval Operational Support Center, which is what the Navy has officially called Navy Reserve Centers since 2006.

On the morning of July 16, Abdulazeez, a 27-year-old naturalized U.S. citizen who was born in Kuwait, fired on the recruiting center in a Chattanooga strip mall and then drove to the Navy reserve center seven miles away. He rammed his car through a gate and entered the facility, shooting and killing five people and wounding a Marine recruiter and a police officer before he was killed by police officers.