In an appearance on CBS News to talk about his new memoir, "Duty: Memoirs of a Secretary at War," Gates said he was often angry during his two stints as secretary of defense under Presidents George W. Bush and Barack Obama, despite his outward calm demeanor.
"So why was I so angry all the time? Why did I want to leave all the time? ... It's just because getting anything done in Washington was so damnably hard," he said.
In his book, he said the majority of Congress is "uncivil, incompetent in fulfilling basic constitutional responsibilities, parochial, hypocritical, egotistical ... too often putting self and re-election before country."
Gates said even the act of getting mine-resistant ambush-protected vehicles produced for the troops in Afghanistan and Iraq was difficult.
"It's bureaucratic inertia," he said. "It's an unwillingness to spend money on a war that everybody expected to be over soon. But the key for me was that protecting these young men and women was foremost."
"I didn't enjoy it," he added. "There is nothing enjoyable about a job where you put men and women in harm's way for their country's sake."