The new U.S.  nuclear weapons doctrine released on Tuesday had stern warnings for Iran and North Korea, with Secretary of Defense Robert Gates explaining that it left "all options on the table" for dealing with atomic renegades despite its broader goal of restricting the U.S. use of its nuclear stockpile.

But Gates also let slip a bit of information that may give pause to environmentalists: most U.S. nuclear missiles are now targeted at the world's oceans.

"Our ICBMs are all targeted right now on the oceans, so that if, God forbid and for the first time in 60 years, there were an accidental launch or a problem would put a missile right into the middle of the ocean, rather than targeted on any country," Gates told a news briefing.

The vice chairman of the Joint Chiefs of Staff Gen. James Cartwright explained the details of  "open ocean targeting", part of a broader package of measures the United States has undertaken for some time to reduce the threat of  nuclear war by mistake.

"For a weapon that has a target associated with it, that is on alert, there is a specific target: that target is the ocean, it is the center of the ocean," Cartwright told the same news briefing,  adding that the U.S. military kept specific areas of the ocean in mind "for that type of work."