Light Signalling Keys
Light Signalling Keys were used to send messages between ships using a telegraph key and a powerful lamp. The British often referred to these keys as "Masthead Keys". Many of the British Masthead Keys had a rotating lever that allowed the operator to put the key in a constant-transmit mode. Some of the later keys had instructions warning the operator not to leave the key down for more than 2 minutes, as it could burn out the lamp.
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