Wampum

The terms of the Treaty of Algiers (March 6th, 1975), concluded between President Saddam Hussain and Shah Mohammad Reza Pahlavi, specific to the Shatt al Arab, was the frontier between Iraq and Iran would be adjusted, including the following of the thalweg (deepest flow) along the entire length of the Shatt al-Arab.

Iraq's stated war aims for its 22 September 1980 attack on Iran, abrogating the Treaty of Algiers, were to recover rights of exclusive navigation of the Shatt al-Arab, to regain several islands, the three Gulf islands of Abu Musa, Greater Tunb and Lesser Tunb, held by Iran since 1971.

The theory of right was the appeal to median baselines (midpoints), rather than deepest flow. The latter was adopted by the United Nations Convention on the Law of the Sea of 10 December 1982 (see Art. 5, Normal baseline, Art. 7, Straight baselines, Art. 9, Mouths of rivers, Art. 15, Delimitation of the territorial sea between States with opposite or adjacent coasts, and Art. 16, Charts and lists of geographical coordinates), and some prior international law treaties such as the 1958 Geneva Conventions on the Law of the Sea.

The choice of mechanism, thalweg vs baseline, has been present in Shatt al-Arab boundary determination for all of the 20th century. In 1932 King Faisal I visited Iran. Shah Reza Pahlavi requested an adjustment of the border according to the thalweg principle, i.e. following the midpoint of the river's narrow and deep main channel of navigation. Faisal refused, and by 1934 Iraq appealed its case to the League of Nations. After the 1936 coup in Baghdad, Iraq agreed to make the border between Iraq and Iran follow the thalweg for four miles opposite Abadan. See the Iraqi-Iranian Frontier Treaty of 1937.

From the accessible page of Hussein Sirriyeh's Development of the Iraqi-Iranian Dispute, 1847 to 1975, a nice one-para backgrounder with a correction and a continuation in []:

The dispute over Shatt al-Arab (the channel constituted by the confluence of the Tigris and the Euphrates and stretching for about 50 miles before it flows into the Gulf) is traceable to the Ottoman-Persian frontier dispute in the seventeeth, eighteenth and nineteenth centuries. It was settled by the [Second] Treaty of Erzurm on 31 May 1847, which gave the Ottomans the right of confrol over the whole Shatt al-Arab. The Ottoman-Persian frontiers were demarcated in 1913 -- 1914 according to a protocol signed in Constantinople in 1913 and a demarcation ... [commission, which wasn't particularly successful and was interrupted by the Crimean War (1854-56), the Anglo-Persian War (1856-57), and the Russo-Turkish War of 1876, as Anglo-Russian colonial conflict completely subordinated Ottoman-Persian conflict. ]

Where Tony Blair enters this mess is in the wanton and willful choice of pretending there is no choice of mechanism, hence there is no boundary dispute, and that the absence of decenial adjustments to the boundary reflecting the natural movement of the watercourse, independent of mechanism (thalweg or baseline), since the Iraq-Iran War, or the better part of 30 years, has no effect in law of determining whether the HMS Cornwall was illegally in Iraqi waters, or illegally in Iranian waters.

As to the lawfullness of acts of belligerency arising over a dispute over the boundary, there is this to consider.

On 9 December 1991, the UN Secretary-General reported the following to the UN Security Council:

That Iraq's explanations do not appear sufficient or acceptable to the international community is a fact. Accordingly, the outstanding event under the violations referred to is the attack of 22 September 1980, against Iran, which cannot be justified under the charter of the United Nations, any recognized rules and principles of international law or any principles of international morality and entails the responsibility for conflict.

Even if before the outbreak of the conflict there had been some encroachment by Iran on Iraqi territory, such encroachment did not justify Iraq's aggression against Iran -- which was followed by Iraq's continuous occupation of Iranian territory during the conflict -- in violation of the prohibition of the use of force, which is regarded as one of the rules of jus cogens.

On one occasion I had to note with deep regret the experts' conclusion that "chemical weapons had been used against Iranian civilians in an area adjacent to an urban centre lacking any protection against that kind of attack.

See also Craig Murray's blog for another well-informed discussion.

There is Craig Murray's set of notes. I don't think he wrote about the choice of mechanism, and may not be aware that from an Iranian (or Persian), or even an Iraqi (or Mesopotamian, or an Ottoman) point of view, subordination of thalweg (mid point of deepest flow), that is, shared navagability, may be both a more rational (or useful) means to partition a shared maritime resource than median baseline from tidal or other fixed point markers, _and_ the better choice of law, being not imposed by the 19th century colonial actors and subsequently re-imposed as "international law".

I suspect that is why Iran will proceed to some law venue, to make the point that the choice of mechanism is not moot because it pleased Saddam Hussein in 1980 and it pleases Tony Blair in 2007.