Hello everyone, despite being a member for many years, this is my first post in the Subsim community. Hopefully it is a helpful one. I have solved the problem with the August 31st, 1939 Enigma message not decoding properly as experienced by Roki. Since this is the first Enigma message encountered at the start of a fresh campaign, for the sake of new players, I put together a little guide to decode this particular message:
EQVI NXVG KFMN VHZJ ZFUD EMPW UPBQ PATK BWUW UGPC LFGW IXIY WAYV LUVX WKHV HSXG SCJX EQVI NXVG
The first part we need to do is isolate the first two groups and we stack them on top of each other in two columns:
EQVI NXVG becomes
E Q
V I
N X
V G
Now we open our Tauschtafelplan folder to find out which Gruppenliste we should use to determine which cipher will be used in decoding. The important thing here is to ensure that we're opening the correct Tauschtafelplan folder for the month the message was sent (in this case, August).
As we can see in the chart below, August is assigned the codeword
Strom. Therefore, we'll change the Tauschtafelplan folder to
Strom. If we do not do this, we will get the cipher gruppe 313 (Potsdam) instead of the correct 247 (Hydra) cipher.
Upon looking in our folder, we have two pages of bigram tables labelled 'A' and 'B' covering all 26 letters of the alphabet. Here we want to find the bigrams that match the two columns of our identifier groups:
E Q
V I
N X
V G
becomes:
E Q = K Q
V I = H M
N X = A Z
V G = I Q
Now we need to figure out which Gruppenliste page we want to use to determine which cipher to use in our decoding. This is done by subtracting the first letter of the first bigram we wrote down:
E Q = K Q
V I = H M
N X = A Z
V G = I Q
Becomes:
E Q = K Q
V I = H M
N X = A Z
V G = I Q
The remaining three letters in the column is what tells us our Gruppenliste. In this case, 'H'. Opening 'H' in the Gruppenliste book, we can see that
H A I = 247. This falls into the range of Hydra (the only cipher operational in 1939).
We now open our Hydra codebook to the correct month and year (Remember, we are using the month the message was sent, not the month we're reading it):
This gives us the settings we'll need to setup our Enigma machine to decode our message:
When we open our Enigma machine, we will need to ensure that we replace the wheels with the correct ones for this message. As shown in the codebook, we will need to place the wheels in this order (the spare wheels are found in the bottom of the box):
B I VIII IV or
B 1 8 4
We then setup our wheels as shown in the codebook.
B we set to
A (default).
I we set to
S.
VIII we set to
E.
IV we set to
N.
We can now close the lid on the Enigma machine and get back to the keyboard side of the Enigma. The second page of the Hydra codebook gives us the plugboard and initial wheel positions for August 31st, 1939. We'll setup our Enigma accordingly:
Once this is setup, we will open up our decoding paper. We then take the four letters from our second identifier group column and type these letters in the Enigma:
E Q = K Q
V I = H M
N X = A Z
V G = I Q
So we will type
Q M Z Q which will then translate to
G D G B. This is the initial starting position of the wheels we will need to set in order to decode our message. This also acts to ensure our settings are correct. If we end up with letters other than
G D G B, our resulting message will be gibberish. In which case, you will need to recheck your Enigma setup.
Now that the Enigma is set with
G D G B, we can type the remainder of our message without the first two identifier groups at the beginning and the end of the message:
KFMN VHZJ ZFUD EMPW UPBQ PATK BWUW UGPC LFGW IXIY WAYV LUVX WKHV HSXG SCJX
With everything done correctly, our message should be displayed in four letter groups, becoming:
ATTACK ANY POLISH SHIPPING ENTERING OR LEAVING THE DANZIG BAY AREA XZZZ
If the message is displaying as gibberish instead, there is an error in your Enigma configuration and you'll have to review the steps to see if anything is out of order.