Acknowledgements I would like to thank my employers QinetiQ for allowing me the use of work facilities to write the first and second editions of this book. I am indebted to Neil Hepworth, who read each chapter as it was first written and gave me such encouragement and sound advice during the creation of this book. I was most fortunate in having so many friends and colleagues who read the book and gave me feedback on it, including Mark Gamble, Cath Hipwood, Ken and Christine Magowan, Steve Mitchell, Michael O'Mahony, Eric Peeling, Thomas Petford, Jutta Spaniol, Sally and David Rees, Rob Rowlingson, Julian