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Enigma Enigma M4 →
Naval Enigma strip printer
Schreibmax, officially known as MZSE or MZSS, is a paper strip printer
for the Naval Enigma cipher machines
M1, M2, M3 and M4, manufactured in 1941 by
Konski und Krüger (gvx)
in Berlin (Germany), exclusively for the German Navy (Kriegsmarine).
It is fitted on top of the Enigma and replaces the lamp panel.
Due to mechanical restriction it cannot be installed on the Enigma I.
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The Schreibmax add-on consists of two units: (1) a power supply unit (PSU)
which is connected to the mains,
and (2) the actual printer which is mounted on top of a Naval Enigma.
It takes the place of the lamp panel. For this reason,
the lamp panel of a Naval Enigma can be removed.
The printer is a small black qubical box, on a metal base plate, that can be
mounted on top of a Naval Enigma machine. Behind the top lid of the printer
is a 9mm paper reel that exits at the top right of the front panel.
The paper is running past a print-wheel and is driven by a
capstan in combination with a pressure roller.
Two keys are present at the bottom: one for
inserting a plus (+)
and one for a space.
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Mounting the Schreibmax on top of the machine is not a straightforward task.
First of all, the light bulbs have to be removed as the printer attachment
has 26 pin-shaped contacts
that take over the function of the bulbs.
More importantly: the printer is attached to the machine instead of
the wooden case lid. For this reason, the printer can only be mounted on top
of a Naval Enigma machine, as it is the only model that allows the
wooden case lid to be removed.
In order to use the Schreibmax with the M4 Enigma, the
4.5V battery has to be removed and the two pins of the external power socket
must be shorted by means of a special shorting plug.
As this plug was missing from our setup, we've replaced it with a
short test wire with crocodile clips.
From the serial numbers of the surviving Schreibmax printers, it is estimated
that approx. 1000 units were manufactured.
Schreibmax printers are extremely rare and are only occasionally on display
in museums. The power supply unit is even rarer and is often missing or broken.
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Without the dedicated power supply, the printer can not be used.
In 2011 we had the unique opportunity to examine the only working Schreibmax
that we know of, at the Foundation for German Communication in Diemen
(Netherlands) [1].
The museum curator, Arthur Bauer, spend many hours getting his unit to work
and his efforts have have eventually payed off.
The image above shows his Schreibmax on top of our
Enigma M4. The yellow plug sticking out at the right
is the connection with the external PSU.
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The Schreibmax consists of a metal frame with the actual printer mounted
on top. The frame physically replaces the top lid of the wooden Enigma case.
For this reason, the lid of the wooden Naval Enigma case was removable.
Before mounting the printer however, the 26 light bulbs of the Enigma must
be removed
and the lamp panel must be made permanently available to the printer.
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This is why the top cover of the Naval Enigma machines consists of two
halves. The part that normally covers the lamp panel can be removed.
After the lamp panel is freed, the printer-frame is attached to the machine
instead of the wooden lid by sliding it onto the hinges.
The underside of the metal frame
contains 26 pin-shaped contacts
that mate with the 26 spring-loaded
lamp sockets of the Enigma's lamp panel, when lowering the printer.
Once in position, the frame is
held in place by two bolts at the front corners of the base plate.
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A rectangular cut-out
in the base plate of the Schreibmax leaves the cipher
wheels accessible, so that the basic setting of the machine can be altered
at any time. The printer-frame is slightly wider than the machine itself,
so that it overlaps at the right.
This is done to accomodate the large 30-pin socket
that connects the printer to the external MZSS power supply (PSU).
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- MZSE
This version is placed aside the Enigma and connects to the machine
lamp panel by means of the wide 26-pin connector (similar to the
MZL Lesegerat). The PSU is marked MZSE, which probably means
Marine Zusatz Schreiber Erika (Navy Add-on Printer Erika).
The PSU has a simple front panel with only a power switch (Ein/Aus),
a red power lamp, and a small window through which the selected mains
voltage is visible (e.g. 220). The small model/serial number tag covers
only the mains voltage window.
- MZSS
This version is installed on top of the Enigma and connects directly
to the lamp panel. MZSS probably means Marine Zusatz Schreiber Streifen
(navy Add-on Printer Strip).
This name is more in line with the page printer MZSB (Marine Zusatz
Schreiber Blatt). It has a larger model/serial number tag,
which covers the mains voltage window and the power switch (Aus).
Furthermore, it has two lids behind which the fuses are located.
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The MZSS power supply unit is a rather complex device which has puzzled
people for a long time. In 2010, our good friend Arthur Bauer [1] finally
managed to crack the mystery when he was restoring his old Schreibmax and
his newly acquired MZSS.
The MZSS supplies power to the printing device but also
protects the switches of the Enigma's keyboard against the sparks caused when
operating the solenoids inside the printer.
He reconstructed the circuit diagram as follows:
In this circuit diagram, the Enigma has been simplified somewhat. As we are
connecting the Schreibmax to the lamp panel, the actual path between the keys
and the lamp contacts goes through the ETW, the wheels, the UKW and back.
In order to keep the currents as low as possible, a relatively high voltage
(115V DC) is used for driving the solenoids. Nevertheless, the solenoids inside
the printer (purple in the diagram) cause enough sparks to cause permanent
damage to the switch contacts of the Enigma. And this is where the extra
circuits inside the MZSS come in.
Each solenoid has a 1K5 resistor (R) connected in parallel and a 1µF capacitor
(C) connected in a network. This so-called Snubber network [3]
suppresses the voltage transients when operating the solenoids and
effectively protects the contacts of the switches by 'killing' the sparks.
As the high-voltage 1µF capacitors used for the Snubber network are relatively
large, they could not be placed inside the printer itself, which is why the
Schreibmax is split in two parts: MZSE (the printer)
and MZSS (the PSU). The Snubber networks are housed inside the MZSS.
As a result, each individual key contact has to be
wired to the MZSS separately. 27 of such snubber circuits are present:
26 for the letters of the alphabet and and extra one for the plus-character
(+) that is available on the printer itself.
All wiring between the printer (MZSE) and the PSU (MZSS)
goes via the large 30-pin connector on the side of the Schreibmax.
All wires of this connector are used:
The drawing above shows the connector at the right side of the printer,
when looking into the receptacle from the bottom.
Two index holes are present to prevent the connector from being
inserted the wrong way around. Please note that this connector carries
220V AC which can be potentially lethal. The pin-out of this connector
is shown in blue in the drawing above.
As there is insufficient space inside the printer (MZSE), the capacitors (C)
and resistors (R) are placed inside the PSU (MZSS).
This is the only reason why
we need so many wires between the printer and the PSU.
The image above shows the wiring diagram of the PSU. All resistors (R) are
wire-wound 1K5 types and all capacitors (C) are 1µF/1000V.
Capacitor (C1) is 375µF/200V.
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The designators MZSE and MZSS might seem a little unusual for the well-organised
German war machine, but they are not uncommon for the Navy.
The following designators were used by the German Navy (Kriegsmarine)
for Enigma add-on equipment:
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MZL
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Marine Zusatzgerät Lampenfeld
External lamp panel for Enigma M3 or M4. Also known as Lesegerät
(reading device).
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MZSB
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Marine Zusatz Schreiber Blatt
Navy Add-on Printer Paper. This was probably an electric typewriter
that could be connected to an Enigma M3 or M4. It printed directly
to a paper sheet.
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MZSE
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Marine Zusatz Schreiber Enigma
Navy Add-on Printer Enigma. This is the basic Schreibmax printer
that is installed on top of an Enigma M4, as shown on this page.
The name MZSE is used on devices with serial numbers below 0200.
Later renamed 'MZSS'.
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MZSS
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Marine Zusatz Schreiber Streifen
Navy Add-on Printer Strip. Strip printer for Naval Enigma.
Used on Schreibmax devices with serial numbers from 0200 onwards.
Also known as Marine Zusatz Streifen-Schreiber.
Previously known as 'MZSE'.
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- MZSE
- MZSS
- Schreibmax
- Zusatzschreiber E.
- Zusatzschreiber Erika
- Zusatzschreiber Enigma
- Zusatzgerat fur Schlüssel M
- Enigma Streifenschreiber
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| | Printer | PSU | Year | Owner |
| • | 0542 | 0204 | 1941 | Private collector, Norway (motor missing) |
| • | 0698 | ? | ? | NCM, USA |
| • | 0831 | ? | ? | NCM, USA (from U-505) |
| • | 0865 | ? | ? | NCM, USA |
| • | 0945 | ? | ? | NCM, USA |
| • | 0987 | ? | 1941 | CDV&T collection, Netherlands |
| • | ? | - | ? | Crypto Museum, Netherlands (under restoration) |
| • | ? | ? | ? | Aeronauticum Nordholz, Germany (fitted on Enigma M3571) |
| • | ? | ? | ? | CSE, Canada (fitted on Enigma M7750) |
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MZSE
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| | Printer | PSU | Year | Owner |
| • | - | 0159 | 1941 | Private collector, Norway |
| • | ? | 0225 | 1941 | NCM, USA |
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© Crypto Museum. Created: Monday 27 February 2012. Last changed: Wednesday, 23 April 2025 - 22:36 CET.
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