5MHZ submerged repeater amplifier, made by Standard Telephones and Cables Limited, England, 1967.
Repeaters (amplifiers) are used in submarine cables in order to maintain the strength of the signals. As the capacity of submerged cable systems increased, valves became impractical for use in repeaters, and long-life transistors took their place. Transistors also made repeaters smaller and lighter. Repeaters would be regularly spaced at intervals along the cables. This repeater has a rigid metal outer casing to protect it.