The French National Gendarmerie has switched on a project running 37,000 desktop PCs with a custom version of Linux.
Stage one of the plan is already online and by summer 2014 the agency plans to move all 72,000 of its desktop machines to open source.
The move is being seen by Wired as another one of those "year of the Linux desktop" things where a huge roll-out in a government department is touted as proof that Windows is dead. Certainly the roll out is similar Linux break-throughs in Germany which were never repeated elsewhere.
The French National Gendarmerie claims the total cost of ownership of Linux and open source applications is about 40 percent less than proprietary software from Microsoft.
This allowed employees to keep using Windows while they got used to the new applications. Only then did the agency move them onto a Linux OS.
It has taken an incredibly long time to get this far. The migration started in 2004, when the Gendarmerie faced providing all its users with access to its internal network.
Moving from Office to OpenOffice was designed to save cash. Then the agency rolled out Firefox and Thunderbird in 2006. Finally, in 2008, it switched the first batch of 5,000 users to a Linux OS based on Ubuntu.
Other governments, such as Brazil, have resolved to use more open source software. China and India even have their own government-sponsored Linux distributions.
However, some government plans to move to Linux are hardly committed. The UK is committed to use open source software "wherever possible", for example. But the majority of its IT budget is spent on proprietary software from companies like Microsoft and Oracle.
Microsoft is also entrenched in many companies who depend on its Active X tech, which only runs on Microsoft's Internet Explorer web browser.