1937 Enigma Manual - English Translation

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I. General.

1. The Enigma encryption machine is a secret object in terms of the secret item regulation (Verschlußsachen-Vorschrift) (II. Dv. 99). According to the regulations of this provision, it is to be kept locked up.

2. Every user of the encryption machine must be aware of the fact that the construction of the machine requires careful usage and maintenance, so that the machine is ready for use at any time.


II. Preparation for Using the Machine.

3. Before starting the machine, it is to be checked for proper operation. For this, the wooden protection box is to be opened, the holding fixture (Picture I, 1) to be opened by lifting the spring-loaded buttons (I, 2), the holding levers (I, 3) to be pivoted down, whereupon the cover plate (I/II, 4) can be opened which exposes the thumbwheel (II/IV,5).

4. The thumbwheels (II/IV, 5) are to be rotated against each other, so that the contacts of the encryption cylinders become bare. Subsequently, the cover plate (I/II, 4) is to be closed and secured by the the holding levers (I, 3).

5. To clean the key contacts, all keys (II, 6) are to be pressed down firmly multiple times, and let snap back rapidly. While doing this, one key is to be held down to avoid unnecessary progression of the cylinders.

6. The battery switch (II, 7) is to be set to „dunkel" (dark) when the battery is fresh. As soon as the battery voltage degrades after long use, the setting „hell" (light) is to be used for improved brightness of the bulbs. Using the setting „hell" too early will lead to premature bulb burn out.

7. In bright sunshine, and to spare the user’s eyes, it is advisable to remove the green Zellon panel (I/II, 8) from the wooden cover by lifting and turning the spring-loaded buttons (I/II, 9), and to secure it on top of the transparent letters using the same mechanism. The Zellon panel attenuates the light of the bulbs and covers all letters so that only the lit letter is visible.

8. For protection against bright sunlight the device can be shaded through pulling the joints of the cover hinge (II, 14) out towards the front, and closing the wooden cover down partially.

9. There is a sheet holder (I, 42) on the inside of the wooden cover that allows documents to be held comfortably in front of the operators eyes during encryption.


III. Setting the Key.

10. The codebook issued with the machine determines the following 4 settings of the device:

  1. Order of the encryption rotors (III/IV, 12) (rotor location),

  2. Setting of the number or letter rings (III/IV, 13) on the 3 encryption rotors (ring setting),

  3. Setting of the numbers or letters visible in the windows (I/II, 16) (initial setting),

  4. Establishment of the connections using the patchcords (II, 30) on the plug board (II, 15) (patch connections).

11. Setting of the keys happens as follows:

The metal cover (II/III, 17) of the device is opened by loosening the two holding bolts (II, 18) through turning, and then lifting the cover at the bolts.

12. The rotors are marked with roman numerals (IV, 34) on the side of the spring-loaded contact pins (IV, 35), and with a number of black dots (IV, 33) corresponding to the numerals on the blank middle part, so that one can check the order of the cylinders without having to remove them.

To establish the correct rotor order (cf. 10a), the holding/release lever in the back left corner (III, 19) is moved to the stop position, and the reflector (Umkehrwalze) is pushed sharply to the left; then the encryption rotors (III/IV, 12) are squeezed together at the thumbwheels (II/IV, 5) to the left with the right hand, and can be removed together with the shaft (IV, 21).

The rotors are put on the shaft in the order defined by the codebook, and inserted into the machine by squeezing them together. When placing the rotors on the shaft, care must be taken that the sides with the polished contact surfaces (IV, 36) always point in the direction of the stop on the shaft (IV, 21a), and that the stop’s (IV, 21a) polished contact surfaces points to the reflector (Umkehrwalze) when inserting the three cylinders on the axle. After insertion of the rotors into the machine, the holding lever (III, 19) is to be folded all the way to the back left.

Removal and insertion of the encryption rotors must happen so carefully that the left bearing pivot does not bend the protruding contact pins of the reflector (III, 20). Furthermore, attention is to be paid that the cylinders rest correctly after folding the holding lever backwards. This can be detected by checking whether the numbers or letters are positioned in the center of the windows (double-check by rotating the encryption rotors).

13. In order to set the correct ring position (Ringstellung) (cf. 10b), the holding springs (IV, 22) of the number or letter rings (IV, 13) are lifted at the button (IV, 23) using the right hand, and the rings rotated with the left hand until the spring-loaded pivot (IV, 24) (which has a red mark starting with machine number 1253) snaps into the hole next to the number as specified by the codebook. The metal cover (II/II, 17) is now closed and fastened using the holding bolts (II, 18).

14. To set the initial state (Grundstellung) (cf. 10c), the cover (I/II, 4) is opened and the encryption rotors (III/IV, 12) are rotated using the thumbwheels (II/IV, 5) until the numbers or letters of the initial state as specified by the codebook are visible in the windows (I/II, 16). The cover is to be closed again.

15. To establish the patch connections (cf. 10d), the hooks (III, 26) on the front panel (I/III, 25) are to be loosened and the front panel is to be flipped down. Thus 26 letter pairs (II, 31) which are labelled with the letters "A" to "Z" and also „1" to „26" are exposed.

The patch cords (II, 14) are pulled out one by one using the plug (do not pull out with the cable!). Then a number of letter pairs is connected to each other using the patchcords as specified by the codebook. Sockets and patchcords are designed distinctively [meaning they only go in the correct way, you cannot plug them in upside down]. Attention is to be paid to the plugs being pushed into the sockets as far as they will go, as to avoid simultaneous lighting up of multiple lights. The front panel is to be closed and to be secured with the hooks (III, 26).


IV. Encrypting.

16. After setting the key (cf. III), the cleartext is to be typed letter for letter by pressing the keys, similar to a typewriter. The keys are to be pressed all the way down, until a letter lights up in the transparent letter display (I, 10) or through the Zellon panel. The next key may only be pressed when the previous key has been released and snapped back into its resting position. Cf. "Schlüsselanleitung zur Chiffriermaschine Enigma" (H. Dv. g. 14) [the manual which details the actual encryption methods] for details on encrypting.

17. If one person conducts the encryption, it is useful writes down the encrypted text with the left hand. If two people are available, one operates the device, and the other reads the letters that light up and writes them down.

18. The instructions in "Schlüsselanleitung zur Chiffriermaschine Enigma" (H. Dv. g. 14) apply for writing punctuation marks, numbers etc.


V. Decrypting.

19. The device is to be set to the specified key (cf. III) and the decryption conducted same as encryption (described in IV), but cipher text is to be typed instead of clear text.


VI. Typing mistakes and failures.

20. If mistakes happen during encryption by pressing the incorrect keys, omitting letters, or double-typing of keys, or through failures of the machine, (lamps not lighting up) the encryption needs to be repeated from the beginning of the message. In that case, the key in the windows must be reset to the initial state. To avoid repeating the whole encryption process, if a mistake happens towards the end, it suffices to press any key as often as letters have been encrypted before the mistake.

Example: if the 32nd letter is keyed in wrong during encryption, after resetting the key in the window, an arbitrary letter is typed 30 times, then the 31st letter is typed correctly to double-check and compare the resulting letter with the resulting letter in the first process. If the comparison results in the same letter that resulted from the first encryption process, the encryption can commence with the 32nd and all following letter in normal fashion.

21. With longer messages the correction of mistakes during encryption is simplified if one writes down the numbers in the windows with every 50th letter. To fix the mistake it now suffices to go back to the last letter where one has a recorded position, to set the corresponding numbers in the windows and to repeat the encryption process from there.


VII. Electricity sources, Lamps.

22. The general user manual (II, 32) is located in the cover of the machine so small problems can be fixed without the manual being at hand.

23. The 4.5 KZT 5 is used as the battery. It is kept in supply by the signal corps supply depot and can be acquired from there. If no usable battery is present, the power posts/leads allow connection from an arbitrary power source (flashlight battery, converter, etc.) however the voltage must not exceed 4 Volts. To use an electricity source on these power leads, the switch is set to "Sammler" [converter].

24. To exchange the batteries in the encryption machine, the cover of the battery box (III, 27) that is accessable after opening the metal cover (III, 17) is to be opened, the exhausted battery pulled out and replaced with a fresh one. Make sure that the contact springs of the fresh battery point to the right (cf. the position of the corresponding contact springs in the battery box [III, 27]).

25. The lamps used in the encryption machine have the following properties: half-spherical shape, 12mm, 3.5 Volt, 0.2 Ampere, soldered acid-fee, and a nickel-coated socket. Ten spare lamps are located on a metal strip (I, 37) on the upper edge of the wood cover. Commercially available flashlight bulbs with 12mm diameter can be used under emergency circumstances, they are to be replaced as soon as possible because they often cause failures.

Starting with machine number 4388 an opening with the lable "Lampenprüfung" [lamp check] (III, 39) is available on the right side of the lamp board (III, 38). Lamps can be checked for usability by placing them into this opening while setting the power switch either to "dunkel" [dark] or "hell" [light]. (Attention: the lamps must be removed from the opening immediately after the check.)

26. Eight patch cables accompany each machine, two of which (I, 31) can be placed into the cover of the machine. Starting with machine number 4388, two sockets (the extreme left and extreme right socket of the center row of the plugboard – III, 41, marked with a red dot) and the lamp labeled "Kabelprüfung" (III, 40) are placed on the left side of the lamp board (III, 38) so that the correct connection of patch cables and their condition can be checked. Both sockets are unmistakable [meaning they only go in one way; one socket is larger than the other] and connected such that the checklamp must light up when inserting the corresponding pins of every plug into these sockets; the patch cable (II,30) is to be wiggled/moved to check it for breakage.


VII. Failures.

27. Failures that can be corrected by the operator are usually contact failures. To detetct and find the failures, it is to be proceeded as follows.

28. To determine whether lamps (V, 43), rotor contacts (V, 44) and short-circuit sheets of the plugboard (V, 45) are in working order, the „Q" key is pressed with any setting of the key, whereupon another letter (for example: „W") lights up. While holding the „Q" key, the key of the corresponding lamp (in this case the „W" key) is pressed, whereby the letter „Q" has to light up after releasing the „Q" key. The „W" key is now held down and, for example, the „E" key is pressed, whereby another letter, for example, „R" lights up. Now the „W" key is released and thus the letter „E" lights up. Then, for example, the „T" key is pressed etc. In this manner, the whole alphabet is checked without changing the key in the window.

29. If, during this test, one of the two corresponding lamps are not lighting up, the following investigation is to be conducted or rather failures to be corrected:

  1. The contact pins of the rotors (IV, 35; V, 44) and the reflector are to be cleaned by turning the rotors inside the machine, or after removal of the rotors from the machine by sanding the contact tabs with sandpaper. At the same time it must be checked whether some of the contact pins are jammed. In this case they must be cleaned with clean gasoline and then lubricated with resin- and acid free oil. Also, the fixed contact areas of the rotors are to be sanded with sandpaper and rubbed with a lightly soaked oil rag every 6 to 8 weeks when the machine is used heavily, otherwise in proportionately longer intervals. All other contact areas, key contacts (V, 46,47), lamp contacts (V, 48) and short circuit sheets (V, 45) are to be protected carefully from oil.

  2. The lamp contacts are to be checked for correct contact by pressing down the lamp’s counter contact (V, 49) while the lamp is removed, and by reinserting the failing lamps after checking both lamps for usability according to section 25. (In case the machine does not yet have a lamp check feature, the lamps are to be brought into immediate contact with both poles of the battery to check them).

  3. The corresponding patch cables are to be tested according to section 26. (In case the machine does not yet have the cable check feature, the cable must be brought into immediate contact with both poles of the battery while using a lamp). If necessary, damaged cables are to be exchanged.

  4. The spring-loaded contact plates (short circuit sheets) (V, 45) are to be pressed away from the plug socket (jack? bushing?) (V, 50) and let snap back by repeated insertion and quick removal of the patch cable plugs (II, 44) into the corresponding sockets pairs (II, 31). (cf. Picture V – inserted plugs at W and E, compared to Q and R without plug).

  5. To clean the respective pair of key contacts (V, 46, 47), the corresponding keys are to be rapidly pressed and released multiple times according to section 5, whereby a third key is continually pressed to avoid movement of the rotors.

Touching the contact areas with the hands is to be avoided by all means.

30. If no lamps light up, the battery is exhausted, or the battery poles do not make contact with the springs of the battery box. Correction of the problem results from insertion of a replacement battery according to section 24, or by bending the springs out so that they make contact.

31. If the failure cannot be corrected as mentioned above, all further repairs are permitted only in the signal corps department, army arsenal or signal corps arsenal according to special rules.
Repairs on encryption machines are strictly prohibited. In this case, the machine is to be sent to the army arsenal (Heeres-Zeugamt) for the domain of the O.K.H. (Oberkommando des Heeres), or to the air force signal corps arsenal for the domain of the Ob. d. L. (Oberkommando der Luftwaffe).


IX. Maintenance of the Machine.

32. The rotor shaft (IV, 21) as well as the bearing areas of the driving shaft are to be lubricated with acid- and resin-free oil every 6 to 8 weeks under continuous use, otherwise approximately every three months. In doing so, it must be carefully avoided to get oil on any contact area (key contacts, lamp contacts and short circuit sheets).

33. To protect the machine against entry of dust etc., the metal cover (II/II, 17) and the cover plate (I/II, 4) is to be kept closed at all times. As soon as the machine is no longer used, the battery switch handle (II, 7) is to be set to "off" ("aus"), and the cover of the wooden box is to be closed.

Berlin on January 12th, 1937.

On Behalf of
The Minister of War
and Army Commander in Chief