http://www.cnn.com/2004/US/09/13/lost.bomb/index.html
"The United States lost 11 nuclear bombs in accidents during the Cold War
that were never recovered, according to the Brookings Institution, a
Washington think tank.
An estimated 50 nuclear warheads, most of them from the former Soviet
Union, still lie on the bottom of the world's oceans, according to the
environmental group Greenpeace."