WASHINGTON -- Secretary of Defense Robert Gates announced Thursday that he's appointed two former heads of the Army and the Navy to review the shootings at Fort Hood, Texas, amid questions about whether political correctness and a shortage of mental health professionals drove the military to keep Army psychiatrist Maj. Nidal Hasan in the Army longer than it should have.

Gates named former Army Secretary Togo West and retired Adm. Vernon Clark, a former chief of naval operations, to lead a 45-day review of the circumstances surrounding the Fort Hood shootings.

Hasan, 39, is suspected of shooting 55 people, killing 13 of them, at the Texas Army base Nov. 5, days before he was supposed to deploy to Afghanistan.

West was Army secretary in the mid-1990s and later became secretary of Veterans Affairs; Clark was the chief of naval operations from 2000 to 2005.

Gates also requested a "more in-depth, detailed assessment whether Army programs, policies and procedures reasonably could have prevented the shooting."

It will be led by Gen. Carter Ham, the commander of the U.S. Army Europe.

The review will go beyond what happened at Fort Hood to examine how the military identifies and addresses soldiers who might be threats to others; the military medical community's personnel practices; and how officials respond to mass casualty events.

A 2007 evaluation written by the top psychiatrist at Walter Reed Army Medical Center, where Hasan was completed his residency, said the faculty was concerned about his "professionalism and work ethic," according to the evaluation, which was first obtained by National Public Radio.

Hasan "demonstrates a pattern of poor judgment and a lack of professionalism," the evaluation said.

Despite that, the Army sent Hasan to Fort Hood, the largest U.S military installation, and he had orders to go to Afghanistan for a year, his first deployment.

The military, like the nation, is battling a shortage of mental health professionals. The Army has only 121 psychiatrists, and overall, the military has about 20 percent fewer mental health professionals than it needs, said Adm. Michael Mullen, the chairman of the Joint Chiefs of Staff.

Some worry that the shortage of mental health professionals, coupled with the hundreds of thousands of dollars the military spent over eight years to train Hasan, may have led the Army to keep him despite the apparent warning signs.