One of the first, but not the very first, according to this guy: www.titanicinquiry.org/USInq/AmInq01Marconi01.php
Senator SMITH.
How long has wireless telegraphy been a practical science?
Mr. MARCONI.
I think it has been a practical science since - you mean in regard to shipping?
Senator SMITH.
In regard to shipping.
Mr. MARCONI.
I should say since 1900. Of course, great improvements have been made since.
Senator SMITH.
Who made the first successful experiment?
Mr. MARCONI.
On ships?
Senator SMITH.
Yes.
Mr. MARCONI.
I think I did myself.
Senator SMITH.
In what year?
Mr. MARCONI.
In 1897.
Senator SMITH.
Since that time have you have found it efficient in cases of a similar character?
Mr. MARCONI.
To that of the Titanic and Carpathia. Yes; I am very glad to say that it has been of paramount utility in a great number of cases.
Senator SMITH.
In what cases?
Mr. MARCONI.
The most important, looking backward, was the collision, which occurred between the Republic, of the White Star Line, and the Florida, near Nantucket; when assistance was summoned; and, fortunately, in that case practically everyone was saved.
Other cases have occurred with other ships. I remember a lightship in the English Channel which was run down over 10 years ago which obtained assistance by the same means; and one of the Cunard liners got into trouble some time ago - a long time ago - and summoned assistance by the same methods. Of course the two important and sensational cases in which it has proved of utility have been the wreck of the Republic, and this disaster to the Titanic.
That senate investigation committee also asked: Since there were water tight compartments in the hull, why didn’t passengers go there? (or words to that effect)