On 30 April this was upgraded to the total exclusion zone, within which any sea vessel or aircraft from any country entering the zone might be fired upon without further warning. The zone was stated to be "...without prejudice to the right of the United Kingdom to take whatever additional measures may be needed in exercise of its right of self-defence, under Article 51 of the United Nations Charter." The concept of a total exclusion zone was a novelty in maritime law; the Law of the Sea Convention had no provision for such an instrument. Its purpose seems to have been to increase the amount of time available to ascertain whether any vessel in the zone was hostile or not. Regardless of the uncertainty of the zone's legal status, it was widely respected by the shipping of neutral nations.
