The fatal shooting Wednesday at Fort Hood, the second in less than five years, has renewed calls for Congress and the Defense Department to end restrictions on servicemembers carrying weapons on post.

According to the Army, the gunman in Wednesday's shooting was carrying a handgun that was not registered at Fort Hood. He was able to kill three before killing himself, and wound 16.

Lawmakers, as well as survivors of the 2009 shooting, claim he could have been stopped sooner if others on base had their weapons by their side.

"When our soldiers are unarmed, they will find themselves in a situation like yesterday and in 2009," Sgt. Howard Ray, a survivor of the 2009 mass shooting in which 13 people were killed, told Fox News.

One source who was at the scene when the Fort Hood lockdown was ordered Wednesday also raised concerns about current DOD policy.

"When will they allow those who have concealed weapon permits to carry them on post?" the individual told Fox News. "We don't have a way to protect ourselves. ... We are all hostages on post."

Military installations largely do not allow soldiers to be armed or carry personal firearms while on post, except for law enforcement and security personnel.

Current Defense Department policy on carrying firearms states:

"The authorization to carry firearms shall be issued only to qualified personnel when there is a reasonable expectation that life or DoD assets will be jeopardized if firearms are not carried. Evaluation of the necessity to carry a firearm shall be made considering this expectation weighed against the possible consequences of accidental or indiscriminate use of firearms. DoD personnel regularly engaged in law enforcement or security duties shall be armed."

The specific weapons policy for Army installations bars soldiers from carrying privately owned weapons unless authorized by a senior commander. Concealed weapons cannot be carried on Army installations even if a local permit has been obtained, according to a spokesman. Further, issued weapons are supposed to be stored in the arms room.

"We hold this position for many reasons," the Defense Department said in a press release Thursday afternoon. "Some of the top reasons are safety concerns, the prohibitive costs of use-of-force and weapons training, qualification costs, and compliance with various weapons screening laws (for example, the Lautenberg Amendment)."

At a Senate Armed Services Committee hearing on Thursday, Army Secretary John McHugh said the investigation into Wednesday's shooting is ongoing and vowed to provide Congress with the facts "as we understand them." He said they view this kind of violence as a "threat across the entire Army."

He said the fact that the shooter, Army Spc. Ivan A. Lopez, was a soldier, and that this happened four-and-a-half years after the last Fort Hood tragedy "only adds to the sorrow." He said the Army is dealing with an "all-consuming sense of loss."

Speaking later in the day, President Obama said that to see "unspeakable senseless violence happen in a place where you're supposed to feel safe ... is tragic."

The shooting Wednesday follows not only the 2009 massacre but also the Washington Navy Yard mass shooting last year. In the wake of that, Rep. Steve Stockman, R-Texas, introduced a bill to allow servicemembers and civilians to carry personal firearms on these installations. He renewed the push for that bill on Thursday.

Rep. Michael McCaul, R-Texas, chairman of the House Homeland Security Committee, said it's time to change the rules.

"We need to harden our military bases so this can't happen, and one possible way to do that is to allow our veterans and active-duty military ... to carry weapons," he told Fox News. "I guarantee if they had ... they could have stopped this guy almost immediately."

Sgt. Alonzo Lunsford, who was shot seven times during Nidal Hasan's rampage in 2009, also said: "If you are allowed to carry a weapon on the base, that's a deterrent."

Others, though, argue the opposite -- that more restrictions would eventually prevent more incidents like this. Democrats in Congress, in the wake of last year's Navy Yard shooting, pushed for more gun control.

At the same time, Defense Secretary Chuck Hagel had vowed to review the physical security at military facilities.

"Where there are gaps, we will close them," Hagel said in September.

Fox News' Justin Fishel and Chad Pergram contributed to this report.