Watch: How US blockade of Iranian ports works - and its risks

As we just reported, Iran-linked tankers have passed through the Strait of Hormuz, despite the US blockade being in place. However, the US is not, technically, blockading the Strait of Hormuz, instead aiming to blockade Iran’s Gulf ports by operating its navy in the Gulf of Oman and the Indian Ocean, rather than risk its vessels close to Iran's coast. The BBC's security correspondent Frank Gardner explains how it will work and its potential impacts across the globe. To play this video you need t