http://book.klll.cc/ebooks/subject/39591.opds 2025-08-15T12:57:05Z Books about Aerial observation (Military science) (sorted by popularity) Free eBooks since 1971. Project Gutenberg https://book.klll.cc webmaster@gutenberg.org https://book.klll.cc/gutenberg/favicon.ico 25 1 2025-08-15T12:57:05Z https://book.klll.cc/ebooks/71934.opds Balloon observation, and instructions on the subject of work in the basket United States. War Department. Division of Military Aeronautics