Cryptologic History Calendar

1939: Army's SIS Translates PURPLE

Friday, September 1, 2017

1939: Army's SIS Translates PURPLE

Description: 1 September 1939: The Army's SIS issued first PURPLE translation.

Excerpt from NSA.gov article - "The solution of PURPLE was a team effort, under the overall direction of William Friedman, with Frank Rowlett leading the day-to-day efforts. Genevieve Grotjan, Albert Small, and Samuel Snyder, junior cryptanalysts, also made important contributions in solving the system.

Once the system had been solved, William Friedman established what may have been the first compartment for intelligence information in the U.S. Decrypts were marked with the codeword "MAGIC" to show they needed extra protection. According to the story, Friedman chose this codeword because he liked to describe his cryptanalysts to outsiders as "magicians."

When SIS personnel had solved the PURPLE system, they came up with the concept of building their own version of the machine for faster decryption, a device they called the "PURPLE ANALOG." An electrical engineer in SIS named Leo Rosen produced a prototype, according to legend, constructed in his basement. Since the Army lacked the machine shop capabilities to make additional units, SIS asked the Navy to make PURPLE ANALOG copies in its facilities."