US naval blockade of Iran includes tracking the 1500 ships in the shadow fleet that operate in the area- WSJ on how the US is doing it. For ships going in shadow ships can disguise their destination, when coming out in these waters it is difficult to do this and the US has good tracking ability. For the US the operation this is something it is already doing in waters of the Atlantic around Venezuela, and which the US has air and sea capabilities of the US Navy.