Engine Order Telegraph

An engine order telegraph, also called a Chadburn, is a communications device that lets a ship bridge order the engine room to run the vessel at a desired speed, without relying on voice or written communication down the length of the ship. Moving the bridge unit handle to a new position rang a bell in the engine room and moved a pointer on a matching dial there; engineers acknowledged the order by moving their own handle to the same position and adjusting the engine accordingly, and ringing the bell three times in quick succession, a cavitate bell, signaled an urgent call for maximum speed even at the cost of a telltale propeller cavitation noise. The device dates from the nineteenth century and remained in widespread use into roughly 1950, typically built around a nine-inch dial with a central pointer and a hand-cranked revolutions indicator. Most modern merchant ships have moved to electronic engine control with remote operation, keeping a mechanical telegraph only as a required backup, while nuclear-powered vessels and submarines still rely on the traditional telegraph because their engineering crews must manually operate steam turbine throttles.