Japan experimenting with new kind of floating mine according to the Dutch newspaper Nieuwe Tilburgsche Courant dated 2 May 1904

An item reported that Japan was experimenting with a new kind of automatic mine floating just below the surface and which was invented by a Japanese. Although the convention of the The Hague, Netherlands did not expressively forbid the use of such mines was Russia against because of the potential threat for neutral ships.(1)

Note
1. At that moment was the war going on between Russia and Japan (8 February 1904-5 September 1905).