Related Rule
Japan
Practice Relating to Rule 70. Weapons of a Nature to Cause Superfluous Injury or Unnecessary Suffering
In the Shimoda case in 1963, Japan’s District Court of Tokyo quoted the 1868 St. Petersburg Declaration and Article 23(e) of the 1907 Hague Regulations, and also referred to the 1899 Hague Declaration concerning Asphyxiating Gases. The Court held, however, that “the use of a certain weapon, great as its inhuman result may be, need not be prohibited by international law if it has a great military effect”. 
Japan, District Court of Tokyo, Shimoda case, Judgment, 7 December 1963.
In its oral pleadings before the ICJ in the Nuclear Weapons case in 1995, Japan stated that it was of the understanding that “the free and unlimited selection of weapons is unacceptable in terms of international law concerning warfare, and that … the infliction of unnecessary suffering … is prohibited, even with regard to weapons that are not expressly banned”. 
Japan, Oral pleadings before the ICJ, Nuclear Weapons case, 7 November 1995, Verbatim Record CR 95/27, p. 37.