TheCodeBreakers
between San Francisco, Honolulu, and Tokyo. Called the A-3, this Bell
Telephone device not only switched the substitution assignments for its
five subbands but inverted them as well. However, of the 3,840 possible
combinations, only 11 were considered suitable for privacy, and of these
only 6 were actually used. They were brought into play in a cycle of 36
steps, each of which remained for 20 seconds, giving the A-3 an overall
period of 12 minutes. It began operating betwee the R.C.A. post in San
Francisco and the Mutual Tel-phone Company post in Honolulu in
December, 1937-and a few days later the Tokyo post, which was still
using the old inverters, asked what kind of system was in use on the
other leg of the circuit, since they could not understand
it. The military took the query as proof that Japan was monitoring the
mainland communications.
It was the A-3 that brought news of World War II to President
annaabi.ee 
