OK I am seeing this error too often in too many blogs and some news reports -- and even a US Admiral who should know better. So let me set you straight: the Strait of Hormuz is NOT "international waters".
That's right, not international waters.
The strait is 21 miles wide. In the northern side, 10.5 miles are sovereign Iranian waters, and the 10.5 miles in the southern side are soverieng Omani waters.
Under international law, such straits are territorial waters of the adjoining nations. The water, the seabed, the air above -- all are sovereign territory of the coastal state.
Ships belonging to foreign countries -- including war ships -- are allowed to pass through such straights, but under limited circumstances known as "innocent passage"...
(Incidental material re: innocent passage has been updated to reflect correction by informed commenator: ships can pass under the new "transit passage" regime adopted by UNCLOS as of 1994 and submarines need not surface. I was wrong on that point.)