I used to work for a defense contractor. MS does offer continued support for XP if your pockets are deep enough. The US Navy has deep enough pockets IIRC. I dunno about anyone on the wrong side of the pond but it's possible they shelled out for it. A different commenters mentioned paying to have an OS maintained indefinitely. That's probably exactly why they're running XP.
Systems like this have the same "we proved it worked correctly once, do you really want to screw with it?" factor as the space shuttle. Proper functionality has been verified with those systems using XP. That goes out the window if you do a major upgrade. All the layers of security you need to implement elsewhere because the OS is fundamentally outdated and insecure is still easier than upgrading the OS. Finally, if an attacker can manipulate those systems then you've already lost. Defense in depth is important but serious defense at these levels is like a "no trespassing, police take notice" sign on the inside of your bank vault above a pile of gold bars.
I agree they probably should have been based on a unix system from the beginning but a lot of these hardware/software system passed the point of no return for the OS portion of their design a decade or more ago when XP wasn't an insane choice. The industry is slowly coming around.
edit: There are a lot of people in here who need to realize that you know very little about the hardware, performance and software requirements of the system. Just because you can write code in the trendy language of the day and use docker to cover up systemic reliability issues that would cripple a LAMP stack does not make you qualified to armchair engineer a software stack that people's lives depend on. This article should make you wonder what set of constraints resulted in them running XP. They did it for a reason. Nobody runs an OS that old without a really good reason.
Systems like this have the same "we proved it worked correctly once, do you really want to screw with it?" factor as the space shuttle. Proper functionality has been verified with those systems using XP. That goes out the window if you do a major upgrade. All the layers of security you need to implement elsewhere because the OS is fundamentally outdated and insecure is still easier than upgrading the OS. Finally, if an attacker can manipulate those systems then you've already lost. Defense in depth is important but serious defense at these levels is like a "no trespassing, police take notice" sign on the inside of your bank vault above a pile of gold bars.
I agree they probably should have been based on a unix system from the beginning but a lot of these hardware/software system passed the point of no return for the OS portion of their design a decade or more ago when XP wasn't an insane choice. The industry is slowly coming around.
edit: There are a lot of people in here who need to realize that you know very little about the hardware, performance and software requirements of the system. Just because you can write code in the trendy language of the day and use docker to cover up systemic reliability issues that would cripple a LAMP stack does not make you qualified to armchair engineer a software stack that people's lives depend on. This article should make you wonder what set of constraints resulted in them running XP. They did it for a reason. Nobody runs an OS that old without a really good reason.