I had much the same experience as many others: very easy for a Grauniad prize but enjoyable, did most quickly; it took me ages to realise what 20d is, but when I got there I thought it very clever. However, there's just one clue that I still don't fully understand: 13a. There's an obvious word that fits, and means a landing or landing zone, but I don't get "B"; or should I say I don't get "zone B"?