to summarise: a blockade is a legal method of warfare, and may be used to prevent not only arms but also food from reaching enemy territory (provided that, in the case of food and other essential supplies, if supply would otherwise be inadequate, the blockading party must provide for their free passage, subject to a right of search)
it is enforceable in international waters, including by searching neutral ships, and attacking and capturing them if they try to break the blockade
and it is lawful if it satisfies paragraphs 93 to 104 … which israel's blockade does
now here's the details …
[attack and capture of neutral ships are dealt with by paragraphs 67 and 146 respectively, and lawful blockade is defined by paragraphs 93 to 104 …]
67. Merchant vessels flying the flag of neutral States may not be attacked unless they:
(a) are believed on reasonable grounds to be carrying contraband or breaching a blockade, and after prior warning they intentionally and clearly refuse to stop, or intentionally and clearly resist visit, search or capture;
146. Neutral merchant vessels are subject to capture outside neutral waters if they are engaged in any of the activities referred to in paragraph 67 or if it is determined as a result of visit and search or by other means, that they:
… (f) are breaching or attempting to breach a blockade.
[N.B. "Neutral waters" are not international waters, they are only the waters of neutral states, see …
14. Neutral waters consist of the internal waters, territorial sea, and, where applicable, the archipelagic waters, of neutral States.]
[a ship is "attempting to breach a blockade" even before it reaches the declared blockade area … see for example paragraph 7.7.4 of the U.S.A.'s Commander's Handbook on the Law of Naval Operations …
7.7.4. … Attempted breach of blockade occurs from the time a vessel or aircraft leaves a port or airfield with the intention of evading the blockade …]
95. A blockade must be effective. The question whether a blockade is effective is a question of fact.
100. A blockade must be applied impartially to the vessels of all States.
[paragraphs 95 and 100 mean that if israel had let the flotilla through, it could then be claimed that the blockade was not effective, and therefore the whole blockade was illegal … this is the main legal purpose for attempting to breach the blockade]
96. The force maintaining the blockade may be stationed at a distance determined by military requirements.
98. Merchant vessels believed on reasonable grounds to be breaching a blockade may be captured. Merchant vessels which, after prior warning, clearly resist capture may be attacked.
israel went through all the necessary procedures, and was perfectly entitled to use lightly armed troops to capture a vessel attempting to breach the blockade
