They take weapons into battle in far-away lands, so why shouldn't members of the US military be able to carry guns when they're off-duty and on home soil?

It's a question that's flared anew in the wake of last week's mass shooting in Tennessee in which four Marines and a US Navy petty officer were killed.

None of the victims had guns at the ready when Mohammad Youssuf Abdulazeez carried out his rampage at two military facilities in Chattanooga before he was killed in a shootout with civilian police.

"Instead of commercial or tourist locales ... he chose 'soft' military targets," said Ali Soufan, a former FBI agent and terrorism expert who has long monitored the actions of al-Qaeda.

"A recruiting center in a shopping mall and a small operations support office (are) very different from heavily guarded bases and forts," he said.

Flamboyant Republican presidential hopeful Donald Trump is leading the charge among politicians for the lifting of a long-standing ban on guns at US military installations.

"Military lives matter! End gun-free zones! Our soldiers must be able to protect themselves! This has to stop!" exclaimed Trump to his 3.29 million Twitter followers.

"Gun-free policies at military facilities have made our men and women in uniform easy targets for terrorist attacks," echoed Ron Johnson, the Republican chairman of the Senate homeland security committee.

Johnson intends to introduce legislation called the Armed Forces Self-Defense Act, calling for the lifting of the military gun ban.

He cited not only the Chattanooga shooting, but also the 2013 Navy Yard massacre in Washington, in which 12 people and the perpetrator were killed, and a 2009 shooting in Fort Hood, Texas that claimed 13 lives.

- Harks back to Newtown -

Such an approach recalls the position of the National Rifle Association, which after the Newtown school massacre in 2012 in which 20 children died suggested that teachers start toting guns to class.

Under a 1992 directive, issued when George Bush senior was president, US military personnel have been expressly prohibited from carrying weapons in their workplaces.

Only those responsible for security or for guarding prisoners are exempted from the rule.

Such measures have historical origins in the Posse Comitatus Act of 1878, which bars local police from calling upon soldiers to maintain public order.

In that sense, American soldiers on US soil are protected by police officers, like any civilian.

That would appear to be a paradox in a country where citizens in 44 out of 50 states can carry weapons in public, as an expression of the Second Amendment's constitutional right "to keep and bear arms."

"For most people in the US military, their job is not to carry a weapon," said Charles Stimson, a Navy reservist and national security expert at the conservative Heritage Foundation think tank.

"If there is a policy change, it would take years to phase in," he said, citing the amount of time it would take for training as well as the fact that many installations are in urban areas.

He added: "We have to take a measured approach and look at the security threat, and if there is a specific threat to any key element of the military."

In Chattanooga's wake, Defense Secretary Ashton Carter has promised measures to reinforce security, but has otherwise remained prudent.

- 'Stricter when appropriate' -

"Services and commanders have the authority to implement stricter security measures they determine appropriate," added a spokeswoman for the US military's Northern Command, which is responsible for domestic security.

The Pentagon made clear its opposition to the idea of weapons at military installations in 2014, citing a number of "complications" including safety, training, "prohibitive cost" and the risk of running afoul of other local or federal regulations.

Oklahoma, Texas, Arkansas, Florida, Indiana and Louisiana have nevertheless taken steps of their own since the Chattanooga shooting to enable their respective National Guard personnel to carry weapons.

"It would help to deter such incidents" as the Chattanooga rampage, but it is "really hard to say" how effective it would be to actually prevent one, said John Goheen of the National Guard Association.

"Even allowing those who serve to have firearms to protect themselves will only reduce the casualty count from attacks," said Ryan Mauro, an analyst at the Clarion Project think tank.

"It won't stop the overall threat. The primary motive of jihadists ... is to earn entry into paradise through violent death," he said.

"If you want to stop the attacks, you need to stop the beliefs driving the attacks."