Enigma Machine

I  have read about these machines from World War II since I was very young, but I had never seen one until I visited the U.S. Naval Academy Museum in Annapolis, Maryland. I first read about this machine in a book I got about 50 years ago.

Kahn, David. The Codebreakers: The Story of Secret Writing. New York: Macmillan, 1967.

It appears from searching on WorldCat.org that the book is rather rare. There is a second edition that is available but used copies of the first edition are listed at over $50 on Amazon. Here is a short summary of the Enigma Machine from Wikipedia:

The Enigma machines were a series of electro-mechanical rotor cipher machines developed and used in the early- to mid-20th century to protect commercial, diplomatic and military communication. Enigma was invented by the German engineer Arthur Scherbius at the end of World War I. Early models were used commercially from the early 1920s, and adopted by military and government services of several countries, most notably Nazi Germany before and during World War II. Several different Enigma models were produced, but the German military models, having a plugboard, were the most complex. Japanese and Italian models were also in use.

I understand that there are a number of examples on display at the U.S. National Cryptologic Museum here in Maryland and I hope to visit that museum soon.