The first successful transatlantic telegraph cable began lasting operation in 1866. It connected Ireland with Newfoundland and made rapid electronic communication between Europe and North America practical for the first time.
Earlier efforts had reached the Atlantic crossing but failed. A cable operated briefly in 1858, carrying messages between Queen Victoria and U.S. President James Buchanan, but its signals deteriorated and the line failed after about three weeks. An improved attempt in 1865 also broke before the connection was completed.
The breakthrough came in July 1866 aboard the enormous steamship SS Great Eastern. The cable was laid from Valentia Island, Ireland, to Heart’s Content, Newfoundland, and the connection was completed on 27 July. Improved cable construction and better electrical methods made the 1866 line far more reliable. It could transmit about eight words per minute, dramatically faster than the 1858 cable.
The year 1858 is therefore a tempting but incorrect answer if the question asks for the first successful, durable service. The 1866 cable established a permanent connection, and the recovered 1865 cable was later repaired, leaving two working lines across the Atlantic.