This Whole Royal Navy Windows Kafuffle

There has been this guy from someplace Making Noise about how the Navy shouldn't start using Windows instead of UNIX in the navy's new Type 45 Destroyer. HMS Vanguard is apparently already running Windows 2000, but I don't know wither what the guy is saying is factually correct or just opinion based.

Ok Windows isn't exactly the most secure OS, but it's easy to develop for and very user friendly, but then I have absolutely no idea what the Navy would want to run on it, because they are obviously switching over for a reason. As switchovers like that cost a lot of money. So you don't do something like that unless you have a clear reason (not that Microsoft would be complaining either way).
*sight* Well as long as Windows doesn't error and fire a nuclear missle at France I suppose I can still sleep at night.