Sgt. Mac's Blog

The Japanese RED BOOK codes, were followed in December 1930 by 85,000 code groups of the so-called  Japanese Naval Codes List, Blue Book. Since no copies of the BLUE BOOK was available, it was left up to the cryptanalyst s to solve it. At the suggestion of Agnes Driscoll, LT. J.G, Thomas Dryer was given the task and solved the problem.

The translated BLUE BOOK codes produced useful information. Messages showed that Japan’s new battleships had speeds in excess of 26 knots, compared to 24 knots for American battleships under construction. Due to this information, the U.S. Navy required their battleships to reach a top speed of 27 knots.

Published revelations early in 1930, stating that progress was being made in solving various code systems, prompted the Japanese, to seek out more sophisticated methods. Almost at the same time, the Japanese Navy sought out an invention by Boris Hagelin, a Swedish businessman. He was in the process of building a commercial cipher machine company, which peaked their interest.

Hagelin was worried that the Japanese would purchase sample machines, then use them to design their own. In the end, he sold them some obsolete machines, invented by his late partner Arthur Damm.

Boris Hagelin was right. The Japanese took the obsolete machines and “reverse engineered” them, creating their own cipher machines. These systems were put to use by the Japanese fleet, Naval attaches and the Japanese Foreign Office.

Their version of Damm’s machine, was called the 91 Siki Angooinziki aka the ’21 model cipher machine.

Sources/Credits:

nsa.gov