Schlüssel M4

German 4 wheel (rotor) Naval Enigma

Schlüsselmaschine M4 and its text-printer 'Schreibmax'

U-boat Enigma type M4



Chiffriermaschine Schlüssel M4 (Four rotor naval enigma type M4). Please notice, that photo quality can be enhanced, by copying an illustration onto your clipboard and then pasting it in Word or WordPerfect or that like



Photo of the enigma: rotor, lamp, key-board and Steckers section. Rotor wheel numbers were counted from right to left. Thus, rotor 4* is at the most left. A bit right of wheel number one we see the 4 volt connector, which could be fed from an external power supply**.  When we closely look at the lock, which is shown partlially in top of this photo, we can see '7027', which equals the machine number. *is the one that does not motion by means of the text-key mechanism, though, that has to be set manually in advance. **otherwise fed from an onboard dry-battery pack  



Rotor type (Römisch) IV, serial number M8260



The lamp cover-plate being removed. 'M' indicates that it concerns a German naval enigma (M = Marine). I once saw in England, that probably due to the lack of appropriate lamps, they had used instead normal spherical types. Which demaged, due to heat and its glass touching, the text paint of the plastic windows. The Germans employed elliptically  shaped lamp bulbs, which are 3.2 volt types. The official voltage was 4 volt (maybe 4.5 volt, when a new dry battery was involved). They expected thus a voltage drop (loss) of about 0.8 volt. The rotor(wheels) compartment is to be locked-off by means of the key, shown right of the rotor-windows. This compartment should, officially, only be accessed by an officer, but on board submarines it was often executed by the (wireless) operator himself. As a code (Schlüssel), thus rotor and 'Stecker' settings, was changed also at midnight, when the responsible officer was (often) off-watch. In 1944 machine settings changed every eight hours. The Germans kept onboard their submarines (U-Boote) always 'German time', which was known as 'DGZ' (Deutscher Gesetzlicher Zeit = Berlin time)**. Today we call this MET (Middle European time)*. Consider also my book on Huff-Duff(Funkpeilungs als alliierte Waffe gegen deutsche U-Boote 1939-1945 *in German = MEZ  **they used, of course, for 'navigation' astronomical related times


Locking key numbered 7027, which equals the machine number

Probably, more rare than an Emigma M4 apparatus is the locking key belonging to it. To my knowledge, it differs from (most) other lock-key types. Its actual overall size is 49 mm, the key bit is 6.5 mm (its hight), with a metal thickness of 1,5 mm . The key is, integrally, made of 1.5 mm Fe plate material



Principle circuitry of enigma.

Most left is shown the reflector unit, which photo is shown next. For better drawing quality, copy this drawing onto your clipboard and paste it in into a Word or WordPerfect or appropriate document



Schlüssel M4, ß (Beta) reflector unit, Serial number M5075. It is wired such, that a lamp current will enter at a particular point and is connected (wired) onto another contact. All depending on its internal wiring (see its schematic principle above)



To operate the paper-tape printer 'Schreibmax' (sometimes known as 'Schreibermax'), the bulbs and the cover-lid of an enigma box has firstly to be removed



The next step is, to place (mounting) the Schreibmax unit at the lid-hinge instead



The text printer Schreibmax being fit. Its contact-pins (see previous photo) are now instead connected onto the contacts of the removed lamps. The actual lamp current* will now activate the printing-hammer-mechanism at an appropriate point(at a certain point of the rotating text-drum). The very complicated power supply is not shown (as we don't have it). *be it, indirectly, as the real printing currents originate from the (separate) power supply



Close-up of the printer section of the Schreibmax attached to the Naval Enigma type M4 (MSZE, Schreibzusatz). The text-drum is in the centre of this photo. Each lamp-contact is linked onto a separately charged capacitor/resistor arrangement. When the text-drum (Schreibrad) is in its appropriate position, a capacitor is being discharged* by means of an electromagnet, which forces the (printing)hammer** to struck (from below) the paper-tape, which then will touch, for a short moment, the (inked) drum section. The two white proceeding key-buttons provide step by step operation, be it one step forward (+) or a free space; as their coded messages consisted always of 'four character groups' followed by a single (free) space#  * 1 out of 26   **from inside the black rectangular box   # the white key-button on the right; like:  ABCD EFGH IJKL M... ....

The main advantage of Schreibmax was, that in contrast to normal operation, enigma could be fully handled by a single operator. Whereas normally two man were involved. One handling the key-buttons and the second man had to read-off the text from the lamp-board (display). However, to my knowledge, most submarines (U-Boote) were not facilitated with such a (nice, though, complicated) device 


Consider also the "Begleitbuch" of  M 4 serial number 15835 and G.kDos. 626 of 20 April 1945



Consider also: The Enigma manual M.Dv. 32/1 (pdf)

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