Sovereign immunity — Public vessels — State-owned corporation — State shipping corporation — Collision in Mediterranean — Actions for damages to ship and cargo, death and personal injury — Whether action based upon commercial activity carried on in the United States — Whether action based upon State-owned corporation's worldwide shipping activities or upon single voyage — Whether collision causing direct effect in the United States — Waiver of immunity — Whether immunity waived by corporation filing conditional claim and answer to be considered only if plea of immunity failed — Foreign Sovereign Immunities Act 1976 — Treaties — Reservations — Status of objection to a reservation — Whether United States objection to a reservation to be taken as forming part of international agreement — The law of the United States