It's been speculated on other Iran threads that Iran isn't militarily capable of closing the straights of Hormuz. I wonder if they could do it through non-military means, ie scuttling some large tankers or other big ships in the navigation channels. I guess it depends how deep it is there. Anybody know?
Here is a map of the Straight of Hormuz, with water depths.
It appears the shipping lanes are about 100' deep.
http://www.lib.utexas.edu/maps/middle_east_and_asia/iran_strait_of_hormuz_2004.jpg