The deadly shooting at one of the region's largest military facilities Monday reopened the debate about whether officials have done enough to secure the nation's massive portfolio of domestic bases.
At least 13 people were killed and several more were wounded, authorities said, when a 34-year-old Texas man and former Navy reservist allegedly opened fire from inside the Washington Navy Yard in one of the most violent such incidents ever on a U.S. military installation.
National security analysts say the Pentagon has improved security at its posts following the 2001 terrorist attacks and, more recently, the 2009 shootings at Fort Hood, Texas. In that case, a radicalized Army psychiatrist shot 13 people to death and wounded more than 30 others.
But the analysts say more could be done to screen military personnel for mental health problems — though it's not clear that such action would have prevented Monday's rampage.
"Given the task at hand, they've done remarkably well," Jeffrey Addicott, director of the Center for Terrorism Law at St. Mary's University in Texas. "If you think about the thousands of people who go on to military bases, it's impossible stop and search every car."
But Addicott said Pentagon officials also need to improve their advance screening of military personnel for signs that they could become violent.
"If you're trying to stop them at the gate, you're too late," he said. "We need to have better screening processes."
Authorities are well aware of the challenge. Just last month, Navy Secretary Ray Mabus ordered the creation of a program to counter "insider threats."
The program, which calls for better training and increased scrutiny of Navy and Marine Corps personnel, is aimed at thwarting not only violent attacks, but also security breaches such as those carried out by Army Pfc. Bradley Manning and National Security Agency contractor Edward Snowden.
Improved mental health screenings was among the top recommendations of an independent panel commissioned by the Defense Department to review the Fort Hood shooting.
Former Maj. Nidal Hasan, an Army psychiatrist who had worked at Walter Reed Army Medical Center in Washington, was sentenced to death last month after admitting to the killings.
The review panel also called for better background checks on civilians who enter military installations and foreign nationals who work for the Department of Defense.
Until Monday, the Fort Hood massacre was the deadliest mass killing on a U.S. military installation — but it was not an isolated case.
Six months earlier, a self-described Islamic radical shot and killed an Army private at a recruiting center in Little Rock, Ark. In March of this year, a Marine killed two officer candidates before killing himself in Quantico, Va.
At a congressional hearing in late 2011, Pentagon officials told lawmakers they had found at least 33 public cases since the 2001 attacks in which "homegrown terrorists" had attacked military installations or planned to do so. An assistant defense secretary, Paul Stockton, told lawmakers at the time that the Pentagon was dealing with the threat.
"Let me provide you with my bottom line up front: The terrorist threat to our military communities is serious, and will remain so for years to come," Stockton said.
Authorities said Monday they are investigating a motive for the shooter, whom they identified as Aaron Alexis of Fort Worth.
Mabus told CNN that Alexis, who was also killed Monday, was a civilian contractor. Records released by the Navy show the New York City native served in the Navy from 2007 to 2011, and worked as an aviation electrician's mate 3rd class at Fleet Logistics Support Squadron 46 in Fort Worth.
The Washington Navy Yard, the nation's oldest military facility, is the central feature of a rapidly developing neighborhood along the Anacostia River in Southeast D.C. More than 15,000 service members and civilians work at the facility.
The Department of Defense counts more than 440,000 buildings in its domestic portfolio located at about 4,400 sites. Generally, visitors are required to show a military ID to enter a base or they are escorted. Vehicle inspections are common.
At Fort Meade, the watershed event for security was not the Fort Hood shootings, but the attacks in 2001, spokeswoman Mary Doyle said. She said the Anne Arundel County Army base did not change its security measures in response to Fort Hood.
Before terrorists crashed planes into the World Trade Center and the Pentagon, Meade was an open base. Motorists were not stopped as they drove through the gates; some used the base as a shortcut between Routes 32 and 175. That changed on Sept. 12.
The attacks "taught us we have to stay vigilant, to report suspicious activity and to be alert at all times," Doyle said. "Like most organizations, we have had active shooter training and annually review what we to do and how to protect yourself."
Chris Grollnek, founder of Countermeasure Consulting Group, said some installations have made more progress on security than others. The Texas-based group has trained private contractors who staff post entries.
"It's not a one-size-fits-all," Grollnek said.
Grollnek said the Army has been proactive in training personnel to deal with on-base shootings. But, he said, trying to prevent incidents before they take place can be tricky because it's usually impossible to identify suspects in advance.
"They're black, they're white, they're men, they're women — no one knows what the profile is," he said.
In the minutes following the shootings on Monday, officials at area installations tightened security.
Fort McNair and Joint Base Anacostia-Bolling, both in the District of Columbia, followed the example of the Washington Navy Yard and ordered personnel to shelter in place.
Fort Meade, Walter Reed National Military Medical Center and the Pentagon also increased security.
Col. Brian P. Foley, the commander of Fort Meade, said he decided to increase gate security out of an "abundance of caution," not because of any specific threat.
"As the events at the Navy Yard unfold, we will remain focused on the safety and security of everyone on Fort Meade," Foley said. "We ask that everyone remain vigilant and report any suspicious activity to local authorities."
A spokeswoman for Walter Reed in Bethesda said the facility had increased security under the direction of Naval District Washington, the command that oversees Navy installations in the area.
A spokeswoman for the Naval Academy in Annapolis said she could not discuss security details.
"The Naval Academy is aware and monitoring the current situation at the Washington Navy Yard," spokeswoman Jenny Erickson said. "We are taking all of the appropriate measures to ensure the continued safety and security of our midshipmen, faculty, staff and our visitors."