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By Phil Stewart
April 3 (Reuters) - The latest shooting at Fort Hood is throwing a spotlight on the U.S. military's so-far frustrated efforts to secure its bases from potential shooters, who increasingly appear to see the facilities as attractive targets.
A soldier with mental health problems killed three people and injured 16 at Fort Hood in Texas, going from one building to another to open fire with a semi-automatic handgun before taking his own life, the military said.
It was the third shooting rampage at U.S. military base in just over six months, with memories still fresh from shootings at the Washington Navy Yard in September and late last month at Naval Station Norfolk in Virginia.
The discussion comes amid a larger debate about how to prevent mass shootings among America's civilian population, an issue that rose to the top of the national agenda after the December 2012 killing of 20 children and six adults at a Newtown, Connecticut, elementary school.
U.S. Defense Secretary Chuck Hagel said the latest incident at Fort Hood showed that there were problems that still needed to be addressed.
Something is not working, Hagel said, "when we have these kinds of tragedies on our bases."
"So we'll identify it, we'll get the facts, and we'll fix it," Hagel told reporters, standing on the flight deck of the USS Anchorage, an amphibious ship, in Hawaii.
Fort Hood itself had already overhauled its own security to better deal with potential "insider threats" after a 2009 rampage by an Army psychiatrist who shot dead 13 people and wounded 32 others. He was convicted and faces death by lethal injection.
Lieutenant General Mark Milley, commander at the base, suggested that the security overhaul helped limit the damage from the shooter, who served four months in Iraq in 2011.
"I think the response from the law enforcement and the medical folks displayed clear lessons learned from the previous case," Milley said, describing a swift reaction by military police to confront the shooter and by medical responders to reach victims.
Just over two weeks ago, Hagel himself unveiled a sweeping review of the Navy Yard shooting, which concluded the rampage that killed 12 people could have been averted if concerns about the gunman's mental health been properly handled.
Hagel endorsed establishing an insider threat management and analysis center within the Pentagon and moving to a system with better monitoring of personnel with security clearances.
In the Norfolk case, a civilian went on base and shot dead a sailor aboard a docked Navy destroyer before being killed.
While some observers question whether shooters can always be stopped, Hagel rejected the idea that nothing more could be done. He called for patience as investigators gather facts.
"We don't have any choice here but to address what happened, and do everything possible to ensure the safety of our men and women who work on these bases," Hagel told reporters.
"It isn't a matter of a question or challenge (that's) too tough. We will do it."
(Reporting by Phil Stewart in Honolulu; Additional reporting by Lisa Maria Garza in Fort Hood, Texas; Editing by Lisa Shumaker)