The U.S. Military drops big bucks for all sorts of equipment, supplies, and software. But while we spend millions to upgrade computers when better software comes out, we also spend millions to keep older software because, if we don't, it could actually cost lives in combat.
The Infographics Show has a good primer on this, available above, but the broad strokes of what's going on are pretty simple to understand.
The Department of Defense is always developing new weapons and programs, and each piece of mission-essential software was originally written for a specific operating system. This is often Windows, the most commonly used operating system for laptops and desktops on the planet.
But, of course, Windows comes out with a new version every few years. So, every few years, the military waits for the worst of the bugs to get worked out of the system, and then it starts upgrading its systems with the newest operating system.
Navy pilots really want the computer to get the thrust right for the catapults since they can be crushed by G-forces or dropped into the ocean if the math is wrong.
(U.S. Navy Petty Officer 3rd Class Ryan Carter)
When computers are being upgraded, though, systems with specialized, mission-essential software are often held back from the software upgrade. If say, the major software controlling the USS Gerald R. Ford's magnetic launch system is optimized for Windows 7, then it would be extremely risky to upgrade to Windows 10 without extensive testing, which the Ford can't do while conducting its mission.
(Note: We couldn't find what software the USS Ford is running for EMALS. This is just a for-instance.)
If the software is changed overnight while the Ford is conducting missions, there's a decent chance that some of the ship's systems won't work properly with the new operating system. That could result in pilots getting pitched off the deck either too fast or too slow for safe flying. Ship defense systems may fail to track an incoming plane or missile, or they could fire defensive countermeasures at a friendly target or when no target is present.
Abrams tanks and many other weapon systems run their own special software and operating systems, but even many of these systems are actually built on top of a Windows OS.
(U.S. Army Mark Schauer)
And this problem exists for all systems that use Windows. And while many weapons, like the F-35 Lightning II and M1 Abrams tank, use special operating systems special-built for aircraft and armored vehicles, some weapons use software that run on "Windows boxes," computers that run specialty software but are built on top of Windows software.
So, you can't safely upgrade the underlying Windows OS without getting new versions of all that bespoke software in the box.
And there are plenty of systems that run in a standard Windows environment. They run programs that control surveillance systems, or that allow troops to pass mission information, or that facilitate training and briefings. Plenty of important briefings run on PowerPoint.
While having your chat windows hacked during combat may not be as dramatic as having your tank hacked, it actually is a dangerous possibility. After all, chat windows are filled with sensitive information during combat and include, things like troop locations, dispositions, armament, etc. And you don't want your enemy hacking into that or stealing it.
So it's probably worth dealing with Windows XP if it makes it easier to prevent intrusion.
But, since the military is using these old software, it needs companies like Microsoft to keep updating security patches for them to prevent intrusions. And the military is often the only customer that needs these fixes, so it single-handedly pays Microsoft to maintain the necessary computer engineers and software coders to do this. And that costs big bucks.