The Enigma was used solely to encipher and decipher messages. In its standard form it could not type a message out, let alone transmit or receive it. From the cipher operator's point of view, it consisted of first a keyboard of 26 letters in the pattern of the normal German typewriter, with no keys for numerals or punctuation. (See diagram below.) Behind this keyboard was a "lampboard" of 26 small circular windows, each bearing a letter in the same QWERTZU pattern, which could light up, one at a time, from bulbs underneath. (The model with an A-Z keyboard, shown in several books on the Enigma, is a Polish-French replica, not an actual Enigma machine.) It measured about 13.5" x 11" x 6", and weighed about 26 lbs.
Behind the lampboard is the scrambler unit, consisting of a fixed wheel at each end, and a central space for three rotating wheels. The wheel to the right of this space is the fixed entry or plate (Eintrittwalze) carrying 26 contacts round its left side, ultimately connected to the keys of the keyboard in ordinary alphabetical order. To the left of the space is the reversing wheel (Umkehrwalze), which scrambles the current it receives and sends it back by a different route from that by which it came. This wheel too has a circle of 26 contacts.
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