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Lawrence   Dick Tracy
Lawrence Secret Code Maker (toy) · 1939

The Lawrence Secret Code-Maker, also known as the Dick Tracy Code-Maker, is a fully functional hand-operated transposition cipher in the shape of a linear wooden slide rule, sold from 1939 onwards as a children's toy by US slide rule manufacturer Lawrence Engineering Service in Peru. 1

The device was intended as a children's toy — for the fun of secret writing — and came with a comprehensive 16-page educational instruction booklet. In reality however, it is a regular shift cipher, which means it can be used just like any other Vigenère transposition or shift cipher.

The device came as a pair of two identical slide rules — one for your best friend — supplied in a carton box measuring 200 x 200 x 13 mm. Sold as an educational toy, it was available for the unbelievably low price of 25¢ 2 making it hard to imagine how the company could survive on it.
Lawrence Secret Code-Maker (complete kit)

Each device measures 195 x 28 x 9 mm and consists of two parts: a fixed U-shaped piece, and a smaller movable part – the slider – that can be fitted in the U-shaped cut-out. Both pieces are made of blank wood and are printed with black ink. The fixed part is printed with Latin alphabets (A-Z) and numbers (0-9). The slider is printed with the same alphabets (A-Z), a row with reversed alphabets (Z-A) and a row with numbers (0-9). At the bottom left, the unit is ambitously marked as Patent Pending, but there is no evidence that the device was ever patented by Lawrence. 3

Lawrence Secret Code-Maker seen from the front. Click for a close-up

It can be used as a regular shift cipher, with a fixed shift, much like the ancient Caesar Cipher, but it can also be used a Reversed Caesar Cipher by using the reversed alphabets at the middle row of the slider, in which case the cipher becomes reciproke (reversible). Like other shift ciphers it can also be used in other – more complex – ways, some of which are explained in the booklet.

Apart from the basic configuration shown here, the same (or similar) device was released as the BEICH Secret Code-Maker that could be won by collecting Beich Whiz chocolate bar wrappers as part of a commercial loyalty scheme. It came with a simplified 4-page booklet. It also surfaced as the Dick Tracy Code-Maker — named after a popular comic strip book character — which came with a simpler 4-page version of the manual. That version is shorter than the original one.

  1. At the time Lawrence Engineering Service was based in Peru, Indiana, USA.
  2. Equivalent to approx. US$ 4 in 2016.
  3. Being a well known transposition cipher, any patent would probably have been declared prior art anyway.

Package Top cover removed Lawrence Secret Code-Maker (complete kit) Close-up of the left side of the slide-rules Right side, with slider displaced to the left Centre part of the slide-rule Close-up of the right side Close-up of the left side
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Top cover removed
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Lawrence Secret Code-Maker (complete kit)
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Close-up of the left side of the slide-rules
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Right side, with slider displaced to the left
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Centre part of the slide-rule
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Close-up of the right side
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Close-up of the left side

  • Lawrence Secret Code-Maker (featured here)
  • BEICH Secret Code-Maker
  • Dick Tracy Code-Maker
Dick Tracy
A shorter version — 6 inches (155 mm) instead of 7.5 (195 mm) — was released in 1961. It was stamped Dick Tracy Secret Code Maker, and was named after the popular comic strip book hero Dick Tracy, created in 1931 by Chester Gold [3]. Like the 7.5" version, it was made by Lawrence.

The Dick Tracy version was distributed by the Chicago Tribune New York News Syndicate as a promotional item. It was sold as a single unit – not as a pair – and came in the simple carton packaging shown in the image on the right, along with a 4-page version of the manual [B].

Photographs in this section kindly provided by Karsten Hansky [4].
Dick Tracy Code Maker with packaging. Photograph kindly supplied by Karsten Hansky [4].

Original Lawrence code maker and Dick Tracy variant. Photograph kindly supplied by Karsten Hansky [4]. Dick Tracy Code Maker with packaging. Photograph kindly supplied by Karsten Hansky [4].
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Original Lawrence code maker and Dick Tracy variant. Photograph kindly supplied by Karsten Hansky [4].
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Dick Tracy Code Maker with packaging. Photograph kindly supplied by Karsten Hansky [4].

Lawrence Engineering Service
Lawrence Engineering Service was a 10-person company, established in 1935 in Wabash (Indiana, USA) and owned by George Lee Lawrence and his wife Vivian C. Lawrence. The company was well-known for the manufacturing of affordable wooden slide-rules for a variety of purposes, such as mathematics, topography, photography, units conversion, engineering, chemistry, music, etc. [1].

In 1938, the company moved to Peru (Indiana), where it existed under the same name until 1947. In that year, after a divorce of the two owners, the company went on as Engineering Instruments, owned by Vivian C. Bozarth (formerly: Lawrence) and her new husband Rev. Frank H. Bozarth. The company existed until everything was destroyed by a major fire on 5 July 1967. Despite the fact that the company was insured, it was decided to close down the ailing business altogether [2].

  • 1935-1938
    Lawrence Engineering Service, Wabash, Indiana (US)
  • 1938-1947
    Lawrence Engineering Service, Peru, Indiana (US)
  • 1947-1967
    Engineering Instruments, Peru, Indiana (US)
For a complete account on the history of Lawrence Engineering, its directors and the many different types of slide rules that were manufactured by them, please refer to The Unique Lawrence, written by David Rance and first published in 2011 for the Oughtred Society [2].

  1. Make your own Secret Codes in a Flash
    Lawrence Engineering Service, Peru, Indiana, USA. 1945.

  2. The Dick Tracy Secret Code maker
    Lawrence/Chicago Tribune, 1961. 4-page booklet.
  1. Slide Rule Museum, Lawrence Engineering Service
    Retrieved June 2018.

  2. David G. Rance, The Unique Lawrence
    2011. Updated 2017. Obtained via [1].

  3. Wikipedia, Dick Tracy
    Retrieved June 2018.

  4. Karsten Hansky, Dick Tracy Code Maker with packaging and manual
    Personal correspondence, June 2018.
Further information
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Crypto Museum. Created: Tuesday 12 June 2018. Last changed: Sunday, 17 June 2018 - 19:05 CET.
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