1956. 80 mW on 20 meters. U.S. to Denmark. Above, the rig that did it.
The online Transistor Museum has a wonderful new article about this historic event, with details on the rig and the operators. Check it out:
http://semiconductormuseum.com/HistoricProfiles/Raytheon_TransAtlantic_Transmitter_Profile_Index.htm
Thanks to AA1TJ for alerting us to this.
First Transatlantic Transistorized QSO
PSE let me know if you come to OZ .. aka Denmark.