Not to be confused with "Castle in the Sky," a Hayao Miyazaki movie that I also have an interest in. This is a BBC TV movie, the story of the invention of radar by Sir Robert Watson-Watt prior to and during the Second World War.
Watson-Watt was a meteorologist, but in the mid-1930s he came up with the idea that you could detect incoming aircraft by bouncing radio waves off of them. With the rise of Hitler and his massive production of military planes, the British War Ministry decided (reluctantly, according to the film) to get Watson-Watt to develop this idea. The movie follows his efforts with a team of other "weather men" and "outsiders" to make their product work as envisioned. Drama is developed (after a fashion) by putting them in conflict with their superiors at the war office who want "real scientists" working on the project, or want the money for more offensive war machinery. And also by having Watson-Watt's marriage fall apart.
They play up that he's a "weatherman" and entirely ignore his background to make him seem the opposite of the Oxford scientists that the war ministry threatens to replace him with - but Watson-Watt did in fact have a very strong engineering background. His marriage did fall apart, although I don't know if it was during the period he was working on this, or because of it. As other critics have pointed out, just because an event is historically significant doesn't make it dramatically significant: Robert Watson-Watt seems to have been a charming, very intelligent, and decent guy, but perhaps not dramatically rewarding. And I have no doubt that the development of radar was a huge struggle full of set-backs, but most of the struggles presented to us were manufactured and not terribly interesting. Eddie Izzard does a great job in the lead (in what may be his first entirely straight role ever?) with good support from a number of the other actors, with one notable exception. I quite like Tim McInnerny, but he seemed like a particularly poor choice as Winston Churchill: he's too tall (18 cm taller than Churchill), not fat enough, and mostly sounded like a frat boy trying to imitate Churchill's speech patterns. Happily, he's not on screen much. In the end a poor story only barely worked for me because I was fascinated by the (limited) technical details of the history.