Windows XP (and ME) still in use in the Royal Navy
I recommend reading this article from The Register about the challenges of updating systems aboard Royal Navy vessels (and the 129 comments that follow it…).
The article reveals that the Royal Navy is still using obsolete versions of Windows, namely Windows ME and Windows XP. How did they find out? Quite simply: the journalist… asked the question while embarked aboard HMS Enterprise.
Crew members confirmed that, since the vessel was built in 2003, most of its information systems date from that period. To be fair, the ship is an experimental vessel. Here it is:

HMS Enterprise
According to the article, this situation is partly explained by the extensive use of Commercial Off-The-Shelf (COTS) technologies and tools rather than purpose-built military systems. On the security side, the familiar sense of “protection” provided by the traditional air gap is also mentioned. While USB ports are reportedly locked down, the article notes that Wi-Fi is available on board for personal devices.