The U.S. Department of Defense's Secretary of Defense is directing all DoD agencies running legacy Windows versions to standardize on Windows 10 and deploy it starting immediately.
The DoD's goal is to upgrade approximately "4 million devices and systems" by February 2017, according to a February 17 Microsoft blog post. (I've asked if this total includes phones, too, but haven't been able to find out so far.)
"I'm expecting all this to happen in a year. To me, this means they know their prior Windows machines aren't that secure and this is of the highest importance. The DoD is typically the last to roll things out as it's viewed as safer and more secure. The opposite is turn now. Hackers are moving so fast, the DoD needs the latest tech to combat it," said Patrick Moorhead, President and principal analyst with Moor Insights & Strategy.