The first protected submarine telegraph cable is…
November 1851 CE
The first protected submarine telegraph cable is laid, across the English Channel, on November 13, 1851.
Having earlier obtained a concession from the French government, in August 1850 John Watkins Brett's Anglo-French Telegraph Company laid the first line across the English Channel, using the converted tug Goliath.
It was simply a copper wire coated with gutta-percha, without any other protection, and was not successful.
The experiment served to secure renewal of the concession, and beginning in September 1851, a protected core, or true, cable is laid by the reconstituted Submarine Telegraph Company from a government hulk, the Blazer, which has been towed across the Channel.