Copper was historically used as the conductor in the first successful electrical telegraph cables.
Copper became the preferred conductor because it combines high electrical conductivity with the ability to be drawn into long, flexible wires. Early submarine telegraph cables used copper conductors insulated with materials such as gutta-percha, a natural latex that resisted seawater.
The first transatlantic telegraph cable was completed in 1858, connecting Newfoundland and Ireland, although it operated only briefly. A more durable transatlantic cable began successful service in 1866. These cables dramatically reduced communication times between Europe and North America.
The insulating material was just as important as the metal conductor. Copper itself conducts electricity well, but direct contact with seawater would cause severe leakage and signal loss. Modern submarine communication cables still use copper conductors in power systems, while fiber-optic cables carry most long-distance digital data as pulses of light.