Maritime Radio Room Clocks

Recently, while doing some research, I found some interesting information about maritime radio room clocks. It seems that their distinctive faces were a result of the maritime radio silence period.

The radiotelegraph silence period (when the radio operator was to listen for distress signals) resulted from the sinking of the Titanic. The regulation was put into effect internationally in 1912, following an International Radio Conference in London, England. Equipment became available just before World War II that could automatically detect a distress signal. Radiotelephone silence periods were put into effect after WWII.

For a hundred years marine distress calls were sent by the Radio Officer (many of whom were hams), on 500 KC, in International Morse Code. In February, 1999 the satellite-based Global Maritime Distress Safety System (GMDSS) replaced the old SOS system.

The maritime radio room clocks used during that period had these distinctive features:

• RED WEDGES: Two red wedges highlighted the three-minute periods of radio silence which were observed twice an hour. During these periods, all transmission was stopped and operators listened for any calls on the International Distress Frequency.
• EXTRA HOUR HAND: Radio clocks were always set to indicate Greenwhich Mean Time (GMT). The extra hour hand could be set to any time the Radio Officer desired, usually the time at the ship’s home port.
• RED BANDS AROUND OUTER EDGE: Red blocks around the edge of the clock dial allowed the operator to time the series of four-second dashes which he could send on the distress frequency to trigger the auto-alarms of nearby vessels. This initial alarm would be followed by an “SOS” sent in standard Morse, and information on the ship’s location and situation.

Much of this info came from the San Francisco Mamritime National Historic Park. Peggy and I plan to visit the park in January.