Sound-powered telephone

Since the microphones used in most telephones are designed to modulate a supplied electric current they cannot be used in sound-powered transducers.

A typical example on a U.S. Navy ship is the "JL" circuit which is used by the lookouts to report visual contacts to the pilot house and the Combat Information Center (CIC).

U.S. Coast Guard Regulations require this emergency communication capability in most vessels today and dictate where phones should be located.

A dial telephone system with a battery backup will not meet the USCG Regulations as they currently exist.

Many different types of equipment have attempted, but have largely failed, to replace the incredibly simple sound-powered telephones on ships.