Amateur radio operators and shortwave listeners are invited to participate in a unique event on August 30, 2025. The Maritime Radio Historical Society’s (MRHS) annual 'cryptographic challenge' will begin at 2000Z. Using the facilities of coast station KPH (San Francisco Radio), an encrypted message, using the famous Enigma machine, will be transmitted in 5-letter groups in Morse and RTTY on 6 different commercial frequencies. Listeners are invited to receive and decrypt the messages. Certificates are awarded for successful decodes. Last year there were 162 participants from 12 countries. More information, including frequencies, can be found on the MRHS website at radiomarine.org. The MRHS was formed on July 12, 1999, the date of the last commercial Morse transmission in the United States.