Microsoft just landed a huge deal to bring Windows 10 to 4 million Defense Department employees

Microsoft just scored a tremendous win with the announcement that the United States Department of Defense will be moving all four million of its employees across all of its agencies to the Windows 10 operating system within a year.

That 12-month timeline is unusually quick for any large enterprise - and especially for the United States government, where bringing in new technology can be painful and take years.

The Department of Defense was apparently attracted by Windows 10's security features, and so hit the gas pedal, according to an official blog post.

Microsoft says that this is going to be its biggest enterprise deal for Windows 10 so far. So far since the operating system came out in summer 2015, Microsoft has gotten over 200 million users on Windows 10 with a goal of getting to one billion within the next two years or so. Big deals like this are an important part of hitting that milestone.

Back in 2013, Microsoft and the Department of Defense signed a similar deal for Windows 8, the much-maligned predecessor to Windows 10. But that deal only affected about 350,000 employees directly employed by the Department of Defense.

This new Windows 10 arrangement accounts for all employees who work at sub-agencies of the Department - which means that it gets the additional benefit of having all its employees everywhere on the same version of Windows. This likely makes life much easier for the DoD's IT department, which has had to manage a mishmash of operating systems across agencies.

As an added bonus for Microsoft, the Department of Defense has certified Microsoft's Surface line of tablets as having met the necessary security requirements, meaning that agencies are free to buy them for their employees. Plus, Microsoft's very cool "Windows Hello" facial recognition sign-on tech is similarly certified as usable for Department employees.

For Microsoft, this is a big deal in all senses of the phrase. Not only will it draw in a lot of cash for Microsoft's Windows business, which has been struggling to gain traction amid a shrinking overall PC industry, but it's a big marketing victory, too. Now, when Microsoft pitches business customers on upgrading to Windows 10, it can point at this deal as a case in point.