Re: @Ben1892
one that you can upgrade from earlier than 8 years after its mainline support ends, worst case, before its extended support ends
Now we are getting somewhere! I suggest there is a very good reason why there are currently systems running Windows for Warships (based on XP) on QE!
Aircraft carriers are big ticket items and don't get commissioned very often. I suspect given the level of co-operation between the UK and US, the QE's systems are based on systems from a previous aircraft carrier (Ford class for which construction started in 2005?).
It would make sense to re-use/build upon existing software, however as noted elsewhere MS really want XP to die, so this platform doesn't have a 50 year future. Also Windows 10 is far too recent for any meaningful (military) applications development to have occurred on it.
So I suggest what has happened is that development to date has largely been focused on XP ie. what is deployed on other carriers, QE provides an opportunity to migrate such software to a new platform. However, to ensure consistency etc. it would be advisable to run both the old and new systems in parallel and compare output - something that can fairly readily be undertaken in the coming years as QE undergoes trials.
So to the causal observer (ie. any one without the relevant security and project clearance) they could see some systems runnng XP and some running something else - without such obvious branding and jump to the wrong conclusion.
Hence I'm more interested on what is seen on QE when she finally enters service in 2020.
Which raises another question, given the lifecycle of Windows 10, it is unlikely to be a Windows 10 derivative, given version 1703 (Creators Update) goes EoL in 2025.