The "Enigma" was the first widespread automatic coding and decoding system.

History of cryptography began already several thousand years before the Enigma was built. Coding methods practiced at that time (e.g. use of non-standard hieroglyphics in Egypt, indication substitution with reverse alphabet in Palestine, shifting codes during Caesar's empire) are naturally very simple - compared with our current knowledge. But these coding methods were substantially extended and refined during the course of the centuries.

But only in the 20th centuries rotor machines - like the mentioned Enigma - played a special role not only within the military, but also in crypto-analysis. Rotor machines code by changing gradually their condition based on a set of known parameters. This is comparable with today's pseudo-random number generator. If the initial condition is known, all subsequent conditions are known as well; thus an encoded message can be decoded again.

The invention of Enigma's internal principal goes back to the American building contractor Edward Hugh Hebern (1869 - 1952), who invented in 1917 a rotary device for a polyalphabetic substitution method using independent alphabets. Strangely enough, the American military did not show interest in its machine.

In 1918 German engineer Arthur Scherbius (1878 - 1929) patented the rotor principle and manufactured in its Berlin company "Cipher Machines AG" a rotor machine, which he named "Enigma". He presented Enigma to the public on several congresses and exhibitions in Berne, Stockholm and Leipzig during the early 20's. Enigma was not held secret at all at this time, because Scherbius tried to market it as "equipment for the transmission of business reports and telegrams".

In 1927 Scherbius bought the patents of the Dutch Hugo Alexander Koch, who had invented a more sophisticated rotor principle in 1919. After Scherbius' death technical developing of the Enigma was further led by Willi Korn.

Internationally seen the interest for a governmental use of the machine was almost non existing. Starting in 1926 the German Reichswehr acquired a larger number of Enigmas. During WWII, Enigma was the most common used but not the only coding machine of the Germans. Strategic messages were coded with a few far more complex machines.

Since 1933 Enigma was used and refined at the Army, the Marine and also the diplomatic service.
Scherbius had already replaced the rotor system in 1928 by a patch board, with which the coding became still more complicated. The operational principle was based on simple electric circuits, of which each connects to a character key of the typewriter like key field with an electrical small bulb, which lights up a letter light up on the indicator field. With each push of a key a new letter lights up.

Each individual electrical path goes through each of three rollers to a front and a rear contact from there to the so-called turn around wheel (Umkehrwalze) and from there again back through all rollers and additionally the plugs of the patch board. The coding scheme used a quite complicated system: in each roller the adjacent entrance and output contacts are not connected with one another galvanically, but they are meshed against each other after a certain system; the setting on the patch board is varied; with each push of a button the rollers are turning after a certain system one position at a time; out of a set of five only three are selected and used in new order; also the initial setting of the rollers is always newly chosen; at each individual roller a shim is adjusted.
During the war, the settings and codes got changed every eight hours. A message could only be decoded if the receiver knew all settings of the sending Enigma. Only then the encoding could be reversed and the plain message could be read. Enemy code breakers not only had to know the mechanics of Enigma's internal construction, but also guess all the different code settings that they received in intercepted messages. That all had to take place in a very short time span, so that a military reaction towards the decoded information was still possible.

During WW II especially England had to suffer under the sea blockade of the German submarines. Intercepted German radiograms piled high at the English secret services, without any chance of decoding them and using this information for a military strategy. First the Polish tried to decipher German intelligence with the help of a calculating machine. This device traveled through France to England where Alan M. Turing tried to construct a larger crypto computer in an organization called "Bletchley Park". The park was hosting the "British Government Communications Headquarter" (GCHQ) with over 200 crypto specialists.
Project "ULTRA" was one of many crypto related installations in Britain. Ultra referred to both the level of security and also budget. With ULTRA the British succeeded in intercepting and decoding German Luftwaffe radio transmissions from May 1940 on, the higher secured submarine code was still unbreakable until 1941.

That changed on May 9 1941 when the German submarine U 110 sank. The British soldiers saved an Enigma from the sinking ship complete with the rollers, signal booklet, code sentences and other immensely important documentation. The captured Enigma was still showing some settings that were used on that day and so Bletchley Park was finally able to decode the radiograms and hand them over to the Royal Navy. With this information the Allies could steer evasive courses away from the German submarine fleet. German Admiral Dönitz had to solve a riddle for himself: he could not explain why from one day to the other the calculated “quota” for each boat, day on sea and sunk tonnage dropped to only 51 tons in January 1943. Despite intensive investigation no explanation could not be found by the Germans. However, each time the German Marine used a more sophisticated Enigma, cryptographers in Bletchley Park encountered a surprising "black out". So e.g. in February of 1942 when a new Enigma with twelve rollers created extended key ranges. Or in 1943 when the German Marine introduced in its Enigma an additional roller and therefore let the scientists at Bletchley Park stand again in the dark for almost 10 months.

After the end of WW II Enigmas were still used in Africa, in the Near East as well as South America. They served in military and diplomatic communication.

With the today's computer technology it might not be difficult to break the Enigma with a plain language attack or brute force attack.