State immunity — Jurisdictional immunity — Whether presumption of immunity — Commercial activity exception — Requirement that commercial activity have substantial contact with the United States — Atlantic Cable Maintenance Agreement — Cable repair ships owned by treaty parties assigned to specific projects — Cable repair ship owned and operated by France assigned to project undertaken by United States corporation on the high seas — Requirement of sufficient nexus between cause of action and commercial activity undertaken in the United States — Action for wrongful death of employee of United States corporation on board cable repair ship on the high seas — Whether sufficient nexus between death of employee and earlier visit of ship and senior crew member to the United States — United States Foreign Sovereign Immunities Act 1976 — The law of the United States