The last person Hitler would want to bomb...

William At War is hilarious.

Not only is it hilarious, it's also great social history. The book opens with Britain on the verge of World War II, and travels through to VE day with William Brown and the Outlaws determined to do their "bit".
He evacuates non-evacuees, foils a Nazi spy plot, and as usual battles and overcomes authority.

It is very funny, and I'm sure that reading it as an adult I enjoyed it a lot more than I would have done as a child when many of the nuances would just have passed over my head. What I most enjoyed about this was the social history aspect - the changes seen through childrens' eyes that the War initiated. It's fascinating, funny, and very readable.