U.S. Secretary of Defense Ash Carter says the military is lifting a ban on transgender service members. “Effective immediately,” he told reporters today at the Pentagon, “transgender Americans may serve openly, and they can no longer be discharged or otherwise separated from the military just for being transgender.”

The fundamental reason for the change, said Carter, is “that the Defense Department and the military need to avail ourselves of all talent possible in order to remain what we are now, the finest fighting force the world has ever known.” Researchers at RAND, he explained, estimate that 25,000 out of approximately 825,000 reserve service members are transgender.

Up to now, trans troops have been “caught in limbo,” he said. He noted that trans troops haven’t been eligible for promotion and their colleagues were required to refer to them by their gender assigned at birth. People who transitioned before trying to enlist were considered unfit for service.”

He also called this “a matter of principle. Americans who want to serve and can meet our standards should be afforded the opportunity to compete to do so.”