Dr Mike Osborne's interest in fortification began with childhood visits to castles It has developed over the years to include all aspects of the topic from Iron-age forts to Cold War bunkers. He was a volunteer co-ordinator for the Defence of Britain Project recording twentieth-century military structures. After a thirty-year career in education he took early retirement to write, producing over twenty books to date. Topics include Civil War sieges and fortifications, drill halls, twentieth-century military structures, a series of county surveys of defences including the award-winning Defending Cambridgeshire, and the best-selling Defending Britain.