Fighting Planes of the World, by Talbot-Booth, Sargent, 2nd Ed., 1940
This small but comprehensive reference book contains over 600 pages of information on the state of military aircraft as of 1940. It is written primarily from the perspective of the British Royal Air Forces. The first ~200 pages describe various aspects of air services. The remaining pages describe the aircraft of each nation's air services, 2 pages per aircraft. The book describes several very rare aircraft of the era, including experimental.
The book is small, 4.25 x 5.5 x 1.25 inches, but packs a ton of information, including a few fold-out pages. Most pages are black and white, with a few color pages for badges and insignia. It is in reasonable but delicate condition and should be handled respectfully.