On July 27, 1866, the first sustained trans-Atlantic telegraph cable was completed. It could just as easily be called Stick To It Day due to the sheer tenacity of entrepreneur Cyrus Field, who affected its completion.

His first attempt, in 1857, was to lay 1700 miles of cable between Newfoundland and Ireland but the cable broke several times and the project was abandoned.

The next attempt, in 1858, was initially successful and was celebrated with the brief exchange between President Buchanan and Queen Victoria. The cable functioned for only three weeks, but it was the first to yield practical results.

The next attempt was in 1865 after the American Civil War, but the cable snapped after 1000 miles.

The mission finally succeeded on July 27, 1866 when the SS Great Eastern laid the first sustained trans-Atlantic cable.

Summarized from Wikipedia.