The History of Hut Eight

iv. WWs (Wetterkurzsignale).

To enable U-boats and others to send weather reports in the shortest possible form Wetterkurzschluessel (Ausgabe 1940) (CI) was brought into use in 1941. It was replaced on 20.1.42 by Wetterkurzschluessel (2. Auflage) (C) and on 10.3.43 by Auflage 3 (C). The principle on which all these books were constructed was the same. They contained table giving single letter equivalents for readings in weather observations; the tables corresponding to the various types of observation made. They will be referred to as WW books 1st 2nd and 3rd edition.

A decoded WW message consisted of a series of weather readings recorded in a particular order (The position of any letter in the decode thus determined which table should be used to interpret it). These readings were followed by the signature of the sender.

A cyphered WW signal consisted of:

Single letter indicator.
Cyphered WW message and signature.

The indicator appeared as the first letter of the first 4 letter group, and between January and May 1942 a trigram preceded to T.O.O.

Three types of WW were used;

a). Obskurzschluessel;
b). Tempkurzschluessel;
c). Pilotkurzschluessel.

b) and c) were sent rarely and were of no cryptographic value since cribbing was not possible. Future remarks refer to a) only.

The number of observations that could be sent in a WW depended on the edition of the Wetterkurzsignalheft in current use and the number of tables it contained. The following list shows how WWs were built up.

Auflage 1940:

1st letter of table 1Latitude in degrees.
2        "    "      " 2Longitude in degrees.
3        "    "      " 3Air pressure to nearest 2 millibars.
4        "    "      " 4Air temperature in degrees centigrade.
5        "    "      " 5Wind direction and strength.
6        "    "      " 6Present weather and clouds.
7        "    "      " 7Visibility.
8 and 9Signature.


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