An engine order telegraph or E.O.T., also referred to as a Chadburn, is a communications device used on a ship (or submarine) for the pilot on the bridge to order engineers in the engine room to power the vessel at a certain desired speed. In its original form, from the 19th century until about 1950, the device usually consisted of a round dial about 9 inches (230 mm) in diameter with a knob at the center attached to one or more handles, and an indicator pointer on the face of the dial. There would also be a revolutions per minute indicator, worked by a hand crank. Modern EOTs on vessels which still use them use electronic light and sound signals.
For urgent orders requiring rapid acceleration, the handle is moved three times so that the engine room bell is rung three times. This is called a "cavitate bell" because the rapid acceleration of the ship's propeller will cause the water around it to cavitate, causing a lot of noise and wear on the propellers. Such noise is undesirable during conflicts because it can give away a vessel's position.
