Wireless message from Theodore Roosevelt to King Edward VII of Great Britain, January 18, 1903. From the Library of Congress Manuscripts division.
January 18, 1903 was a cold, clear night at the Marconi station at Wellfleet, Massachusetts. Guglielmo Marconi was pleased by the weather as he was about to make history with his wireless telegraphy once again. It was on this perfectly clear night that Marconi transmitted the first trans-Atlantic wireless radio message.
Marconi had been slowly lengthening the distance his messages traveled from the beginning of early December. This trans-Atlantic message was going to be the crowning achievement of his new technology. President Roosevelt was, of course, in the thick of things. His message to King Edward of Great Britain was the first successful trans-Atlantic message ever sent and he took the opportunity to note the great scientific triumph and to send greetings to Britain from the American people.
While these successful transmissions were a boon for Marconi, his invention proved its usefulness only a year later on January 23, 1904 when the Republic, an ocean liner, collided with another ship and began to sink. Its wireless operator got an SOS message out and led to a nearly complete rescue of all passengers. This use of his invention would make Marconi a popular hero.
Mass Moments: Marconi Transmits Radio Message. Massachusetts Foundation for the Humanities.
Fessenden and Marconi: Their Differing Technologies and Transatlantic Experiments During the First Decade of this Century. John S. Belrose, International Conference on 100 Years of Radio -- 5-7 September 1995.