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.”