Ever since seeing these 'Maunsell forts', while on a fishing trip, I've been fascinated by them. They've put in an appearance in Cowl and now, sort of, in The Departure. They came up in a chat on Twitter about that book (about the stinking reviews on amazon). In the book they aren't there but in their place is Maunsell Airport ... in fact Boris Island Airport. Thanks to David Hutchinson for the link to this video clip.