Israel's attack on the MV Mamara, a Turkish vessel, means they just attacked a member of NATO. According to the NATO Charter, Article 5
The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and consequently they agree that, if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defence recognised by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area.
If you think there is wiggle room in that definition, you would be mistaken. Article 6 is explicit about where attacks will trigger responses. Vessels in the Mediterranean Sea are mentioned explicitly.
Article 6 (1)
For the purpose of Article 5, an armed attack on one or more of the Parties is deemed to include an armed attack:
on the territory of any of the Parties in Europe or North America, on the Algerian Departments of France (2), on the territory of or on the Islands under the jurisdiction of any of the Parties in the North Atlantic area north of the Tropic of Cancer;
on the forces, vessels, or aircraft of any of the Parties, when in or over these territories or any other area in Europe in which occupation forces of any of the Parties were stationed on the date when the Treaty entered into force or the Mediterranean Sea or the North Atlantic area north of the Tropic of Cancer.
(1) The definition of the territories to which Article 5 applies was revised by Article 2 of the Protocol to the North Atlantic Treaty on the accession of Greece and Turkey signed on 22 October 1951.
(2) On January 16, 1963, the North Atlantic Council noted that insofar as the former Algerian Departments of France were concerned, the relevant clauses of this Treaty had become inapplicable as from July 3, 1962.
If the former Soviet Union had attacked a NATO vessel in the Mediterranean, we know what would have happened. Of course, that never happened for obvious reasons. In fact, Article 5 was never invoked until the attack on the WTC and the Pentagon on Sept. 11, 2001. After 9/11, the US invoked Article 5 for the first time in the history of NATO. That's why NATO forces are still in Afghanistan.
Attacking vessels on the high seas is not the sort of thing people ignore. When the PLO boarded a vessel (the Achille Lauro) and took it over, killing one of the passengers (Leon Klinghoffer), the UN responded by redefining piracy. Nations cannot be guilty of piracy -- by definition. However, this certainly seems to be a criminal act at a minimum. Some might even consider it an act of war. The question now is whether an Israeli attack on the MV Mamara, a Turkish vessel, and thus a vessel of a NATO member, in the Mediterranean Sea leads Turkey to invoke its rights under Article 5 of the NATO Treaty.
The US media has been very slow to cover this early on, while Europe and even Ha'aretz were giving this front page coverage. Unlike previous situations (e.g. the attack on the USS Liberty in 1967) we have immediate access to international media and they have access to individuals on the scene. I expect this story to run away from the Israelis pretty quickly regardless of their inevitable claim this was a "defensive" action. This certainly has the potential to develop into an ugly confrontation.
UPDATE I This is no longer an academic discussion. According to the Economic Times:
NATO will hold emergency talks on Tuesday at Turkey's behest after the deadly Israeli raid on a flotilla of aid-carrying ships bound for Gaza
UPDATE II CNN-IBN (a partnership between Global Broadcast News (GBN), a Network18 Company, and Turner International (Turner) in India) is reporting
Turkey threatens action; Israel on alert
Two Turkish activists were reported to be among those killed in the flotilla. Ankara warned that further supply vessels will be sent to Gaza, escorted by the Turkish Navy, a development with unpredictable consequences.
UPDATE III: As of 2:00 PM EST, the White House has issued no statement I can find regarding this incident except for the following "Readout of the President's Call with Prime Minister Netanyahu of Israel"
This morning between 10:00 and 10:15 AM CDT, the President spoke by phone with Prime Minister Netanyahu. He said he understood the Prime Minister's decision to return immediately to Israel to deal with today's events. They agreed to reschedule their meeting at the first opportunity. The President expressed deep regret at the loss of life in today's incident, and concern for the wounded, many of whom are being treated in Israeli hospitals. The President also expressed the importance of learning all the facts and circumstances around this morning's tragic events as soon as possible.