El asunto Tornasol
"German Research" discusses various German secret weapons of World War II, with an emphasis on airplanes, rocketry and the Germans' research methodology. It was first published in 1947. The book has become a collector's item in Europe since Hergé featured it in the storyline of "The Adventures of Tintin" comic "The Calculus Affair", published in 1956, where it appears on page 23. The book is available, nevertheless, in various versions. Hergé censored the swastika, when he inserted the book.