This is a rare photograph of a field communications center showing a soldier using a wooden slide rule transposition cipher device. A number of EE-8 telephones can be seen lashed to the uprights of the truck, as well as a lineman's safety belt and other paraphernalia of field communications. (Photo by Bernard Hoffman. Originally published by Acme and Cleveland Press News, Official Life Magazine Photograph).
This is an enlargement of the slide rule device. (Above text and photos courtesy of Snyder's Treasures < email@example.com> . This item was put up for sale on E-bay).
Stephen A Kallis, Jr. offers some background information. "The generic name for such gadgets is the St. Cyr Slide (or Sliderule). It's a useful tool for beginning cryptanalysts. It can be used for polyalphabetic systems such as Vigenere messages as well as for simple substitution".
These units were about 8 - 10 inches long,
and came two-and-a-handbook per set. The Lawrence units were called "Secret Code Makers," and were popular in the 1930's and 1940's. (Photo courtesy Stephen A Kallis, Jr.)
The entire device. (Photo courtesy Stephen A Kallis, Jr.)