On the Legality of Executing a Blockade in International Waters

It's come up in the comments, and Galrahn at Information Dissemination, who is arguably one of the most knowledgeable about things Naval out there, nails the issues of maritime law when he says that, "Israeli Actions Are Stupid, But Legal.

He notes that armed stop and seize operations in international waters have always been legal, they are routine operations in US anti-drug operations, for example, and Israel had declared a blockade, and a blockade area:

Under international law, the consensus of the maritime attorney's I have spoken to is that the boarding operation by Israel was legal. The coast of Gaza has been under maritime blockade by Israel, a blockade that was well known - indeed running the maritime blockade for political purposes was the specific intent of the protesters. It is why the press had been reporting all week that the situation was likely leading towards a confrontation. Is anyone surprised that Israel had an established maritime blockade and enforced that maritime blockade? I'm certainly not, Israel made clear all week that the flotilla would not be allowed to pass.

The maritime blockade is a result of the war between Israel and Hamas. Ones political position on that ongoing war is completely irrelevant to the reality that the maritime blockade was established. Knowledge of the maritime blockade by the protesters is also not in debate, and neither is knowledge the flotilla intended to violate the blockade - they made this clear themselves in the press. Once the flotilla made it clear in the press they intended to run the maritime blockade, according to international law, and even US law, the flotilla was considered to be in breach by attempting to violate the blockade.

………

The truly scary part is that under international laws governing maritime blockades, Israel could have outright sank the ship instead of board it as an alternative enforcement of the maritime blockade, and Israel still been within their rights under international law. Such an action could have led to war with Turkey, but even if the ship would have been sunk, Turkey would still be on the wrong end of international law in this situation. Turkey will likely find plenty of populist political support in NATO countries over these events, but if they attempt to escalate they may find that support is fleeting among their NATO allies.

(emphasis mine)

It is that last paragraph that makes it clear just how f%$#ed up everything is.

You can argue over whether the blockade is an illegal mass punishment of the population (illegal), or an attempt to deny war materiel to Hamas (legal), but the execution of a stop/search/seize order in a declared blockade zone even if that zone includes international waters, is clearly legal.