This example of the Swiss K Enigma was supplied to the Swiss government in 1938, 1939 and 1940 for use by their Army and Air Force. Given that Switzerland was neutral during WW2 it is likely that these machines were supplied as a gift so that relations between the countries could be kept on an even footing much as was the case with the banking sector.
The Enigma K is the commercial version of Enigma without a plugboard and fitted with only 3 rotors. What looks like the 4th rotor is actually a reflector. It has the same thumbwheels as the rotors because it is settable as part of the daily key. After it is set, it doesn't move during use.
The K model was derived from the commercial Enigma D (A27), which came into production from 1927, the D being provided to the railways of Germany and other friendly powers including Spain (during the Spanish Civil War, 1936-39), Italy and Switzerland. The Swiss made their first order for the Enigma D in 1938 when they ordered 14 machines, a further 39 machines in 1939 and finally two further batches in 1940, giving them some 265 machines in total, 102 for the Swiss Army and 163 for the Air Force. The additional light panel was supplied by a Swiss firm and incorporated into the large carrying case, which is of Swiss manufacture. The light panel is wired directly into the machine and makes it possible for a second operator to decode the more secret messages! The final variation from the standard Enigma D, is the power transformer, supplied by another Swiss company making it possible for 4 machines to be working off the same transformer.
Interestingly enough the French broke the Swiss Enigma K in 1941, the Allies soon after, and the Germans had been reading the diplomatic and military messages since 1939 (even though the Swiss had rewired the machines as soon as they received them). Because the code had been broken, the Swiss developed a new machine the NEMA, which didn't come out until 1946.
Enigma-K3 (Photo courtesy Bonhoms Auction House)
Contributors and Credits:
1) K3 copy via Bonhoms Auction House