Set of four German technical publications (spying) on U.S. aviation, 1933-34: PART 1: Impressions from Military Aviation, 38 pages with 4 real photo pages; PART 2: Institutes, Societies and Special Facilities, 22 pages, 2 real photo pages; PART 3: Aircraft Manufacturers, 30 pages, 4 real photo pages; PART 4: Aircraft Engines, 42 pages, 5 real photo pages. Fascinating and unique set of technical spying documents published about the time of Hitler's ascension to power in Germany. The two authors traveled throughout the U.S. gathering technical data on the state of U.S. aviation. A search of eight international bibliographies by professional reference librarians showed no holdings. Good-very good condition with period German library markings. A unique and extremely rare set.