It was not a radio at all. It was an electro-mechanical coding machine.

Simply put, the machine was set to the proper setting by installing and rotating several rotors into a pre-agreed upon position. At first there were three rotors and later four.

Later models also had a plug board attached where "phone plug" wires could be plugged in also in a pre-agreed upon pattern.

Each of these rotors and plugs completed a unique series of circuits.

When a letter/number key was pushed down, a circuit was made (actually it ran twice through) and lit up another letter/number. This was the encoded letter/number that would then be transmitted over the radio in the usual way.


Here is a good starting source [en.wikipedia.org]

There were many different models of Enigma and some worked a little differently than the others.

It is important to note that the Enigma started out as a commercial encoder sold to the public in the 1920s.

It was deemed so secure that it should not matter if your enemy had an enigma machine, they still should not be able to decyper your message.

The primary weakness of the enigma rested with the operators. There were cases of operators not bothering to change rotor settings or using predictable rotor settings due to lazyness. This gave the code breakers some help.