"Today we have a new policy set by our new president. We have a new strategy, a new mission and a new ambassador," Gates said. "I believe that new military leadership also is needed."
The decisions were made after consulting with the U.S. Navy Adm. Mike Mullen Joint Chiefs of Staff chairman -- also at the news conference -- and Army Gen. David Petraeus, Central Command commander, and President Barack Obama's approval, Gates said.
"I believe my decisions are in the best interest of our national security and the success of our mission in Afghanistan," Gates said, urging swift Senate confirmation of Gens. McChrystal and Rodriguez.
Timing for replacing McKiernan made sense because the new policy, strategy and mission in Afghanistan were just beginning.
In that context, "I emphasize that the focus here is simply on getting fresh thinking, fresh eyes on the problem and in how we implement the strategy and mission going forward," Gates said.
He stressed "nothing went wrong" during McKiernan's 11-month tenure as commander of U.S. forces in Afghanistan.
Both McChrystal, director of the Joint Chiefs, and Rodriguez, a military assistant to Gates, have experience in counterintelligence, Gates and Mullen said.
"I have said that we must focus all of our effort in terms of making Afghanistan better," Mullen said. "There probably is no more critical ingredient than that of leadership."
Notable deaths of 2014 [PHOTOS]