This history of the U-2's replacement provides an accessible overview of the A-12's development and use as an intelligence collector. The author has tried to make the narrative informative to lay readers while retaining enough technical detail to satisfy aeronautics and engineering readers. He has used sources listed in the bibliography and extensive files on the A-12 program in CIA Archives. This book has been augmented with a few recently declassified documents, including the designer's own history of the project and a list of other documents now available to readers via the Internet thanks to the Freedom of Information Act. (David Robarge was the CIA Chief Historian when he originally published "Archangel" as a 67-page book in September, 2007. Nearly 100 pages of additional documentation has been added as parts 2-4 to produce the present volume.)