Virtual Lorenz SZ40/42

A virtual simulation of the German World War II cipher attachment

Find Out More Run Virtual Lorenz Try Paper Lorenz

What is a Lorenz SZ42?

During World War II, the German High Command required a fast and secure way of transmitting messages between themselves and the army commanders out on the battle fronts. C. Lorenz AG in Berlin created a set of cipher attachment machines, the Lorenz SZ40, SZ42A and SZ42B, which could encode messages directly from a teleprinter and transmit them via radio to a duplcate machine at the receiving end where the original message would be decoded automatically.

This website has an online simulation of the Lorenz machines so you can actually encipher and decipher secret messages, exactly as they did during the war.

What do I need to know to run it!
Instructions for use


Use your browser zoom to see the big picture or to look a little closer.

PC: Use Ctrl with +/- or with 0 for 100% or use Ctrl and mouse wheel
Mac: Use Command and +/- or with 0 for 100%
Tablet/Phone: Just pinch zoom as normal

Click or swipe dials and switches

Try clicking the switches or keys.

If you have touch screen, try opening the cover of the Lorenz by pressing the lock image and swiping each wheel to set them.

Look for Info Boxes

Look for the helpful blue info boxes. These give extra information about panels you can interact with and some options and selections.


Check out the tutorials in the top menu on the Lorenz emulator page.

These will give you an idea on how the Lorenz SZ was used.

What does it do?

Credits and links

A number of people I need to say thanks and tip my hat to... .. The National Museum of Computing where my obsession was sparked! .. Bletchley Park

Heinz Nixdorf MuseumsForum .. Heinz Nixdorf MuseumsForum

The Bill Tutte Memorial Fund .. "Bill Tutte achieved one of the greatest intellectual feats of World War Two by breaking the extremely complex Lorenz code without ever seeing the machine that generated it."

Captain Jerry Roberts and all the codebreakers in the Testery. Without these people's code breaking skills and their daily breaking of the Lorenz wheels, Colossus would have been unable to function.

Frode Weierud's .. for his assistance answering questions and especially his site's Lorenz operating manuals!

FuseMetrix Group .. My employers who put up with me nattering about Colossus and allow me space on their servers to run this website!

Let me know what you think!

Have I got something wrong, it doesn't work quite correctly on your computer or maybe you just want to say hi - find me on Twitter or check my Facebook or Twitter pages

Martin Gillow