Continuing in that vein, Gates told the New York Times, "I will always be an advocate in terms of wars of necessity. I am just much more cautious on wars of choice."
Gates expressed skepticism about the United States' intervening militarily in Libya.
A common theme in Gates' farewell interviews has been what he considers to have been his main accomplishment as defense secretary: getting the troops what they needed to do their jobs safely as quickly as possible.
He told PBS' Jim Lehrer, "I'm proudest of what I've been able to do for our troops, giving them these heavily armored vehicles, these Mine Resistant Ambush Protected vehicles; giving them one-hour medevac or less in Afghanistan; more reconnaissance capabilities to prevent them from being attacked; trying to do whatever was necessary to help them accomplish their mission and come home safely."
At his final news conference last week, Gates thanked journalists for raising public awareness about the heavily armored MRAP vehicles and the health care shortcomings for wounded warrior outpatients at the Walter Reed Army Medical Center.
"Responding to both of these critical issues, which only came to my attention through the media, became my top priority and two of my earliest and most significant management decisions," he said.
Gates cut through the Pentagon's bureaucracy to get the MRAP's into rapid production and out into the field to protect service members from the roadside bombs that scourged Iraq and Afghanistan.
Ultimately, 27,000 of the heavy vehicles were produced for service in Iraq and Afghanistan. The Walter Reed episode showed Gates' steely decisiveness in putting leaders on notice that they would be held accountable.
In the Walter Reed episode, Gates quickly fired the secretary of the Army and the surgeon general for the substandard care highlighted in media reports. Gates also fired the Air Force's top two leaders after a series of missteps involving nuclear weapons.
Asked by the Associated Press what he will miss the most when he leaves his job, Gates responded, "One is the people that I work with, and the other is the troops. I won't miss anything else."
In retirement, Gates said, he plans to write two books, one a memoir about his years at the Pentagon and the other a humorous take on how to reform "large public institutions."