This style of Ship Order Telegraph was used on ships (and submarines!) from the 19th Century until around 1950. A communication device, it was used to send directions about altering the vessel’s speed from the pilot on the bridge to the engineers in the engine room. This was done by the pilot moving the lever to a different position on the dial, triggering a bell in the engine room. The engineers would acknowledge the order by moving their lever to the same position and would then adjust the speed accordingly.