Nov 27, 2018:  From our friends at Southgate Amateur Radio News.

It was on the night of 27th November 1923 that the first Trans-Atlantic short wave radio contact was made. It took place between radio hams: Leon Deloy (8AB) in France and Fred Schnell (U1MO) in the USA.

This first short wave Trans-Atlantic contact represented the culmination of many tests and attempts to hear and then make contacts across the Atlantic.

The contact pushed forwards the technology used, not only by radio amateurs but other users as well.

After the First World War, it took some time before British radio amateurs were allowed back on the air, and as a result of restrictions and for many other reasons, the equipment available was limited. This forced the use of improved technology and techniques. That said, the first contact was made between the USA and France, but Britain also succeeded and went on to make the first contacts with the Antipodes later.

Read the whole story here:
https://www.electronics-notes.com/articles/history/amateur-ham-radio/first-transatlantic-contacts.php