Coral (cypher machine) in the context of Stepping switch

In electrical engineering, a stepping switch or stepping relay, also known as a uniselector, is an electromechanical device that switches an input signal path to one of several possible output paths, directed by a train of electrical pulses.

The major use of stepping switches was in early automatic telephone exchanges to route telephone calls. Later, they were often used in industrial control systems. During World War II, Japanese cypher machines, known in the United States as CORAL, JADE, and PURPLE, contained them. Code breakers at Bletchley Park employed uniselectors driven by a continuously rotating motor rather than a series of pulses in the Colossus to cryptanalyse the German Lorenz ciphers.