On September 14, 1937, the Nion Agreement for the Protection of the Mediterranean Trade was signed. After the outbreak of the Spanish Civil War in 1936, Britain, France and other 27 European countries announced a policy of non-interference against Spain, which jointly invited Germany, Greece, Turkey, Soviet and other countries to meet on the Spanish coast in order to prevent the ship's transport of weapons. The Italian submarines fought against submarines of "unknown nationality" in the Mediterranean Sea and refused to participate. On September 14, 1937, the Nion Agreement was signed with the representatives of Britain, France and other seven countries to compensate for the ship's territory near Geneva. The Nion Agreement also stipulated that when the Spanish Navy was used in the sea against any of the above