State immunity — Jurisdiction — United States forces stationed in Italy under NATO Treaty, 1949 — Low-flying military training flights — Whether constituting sovereign activity — Proceedings brought before national courts to restrict such flights on safety and human rights grounds following accidents involving loss of life — Whether United States entitled to jurisdictional immunity — Potential conflict between human rights protection and rule of jurisdictional immunity excluding recourse to courts — Immunity for acts performed jure imperii

Relationship of international law and municipal law — Customary international law — Jurisdictional immunity of foreign States for acts performed jure imperii — Whether constituting rule of customary international law automatically incorporated into municipal law — Italian Constitution, Article 10 — Whether such rule taking precedence over right to effective remedy before national courts — The law of Italy