Why Iran can threaten the Strait despite weak navy

Iran's effective closure of the Strait of Hormuz has entered its third week and with that, shipping has been put to a halt - hampering a fifth of the world's oil supplies.

US President Donald Trump has urged its allies and China to send warships to the Strait to help secure the key shipping route out of the Middle East.

But the US is yet to do so - so will any other nation offer its own navy?

• GUEST: Bryan Clark, senior fellow and director of the Center for Defense Concepts and Technology at the Hudson Institute in Washington and formerly a special assistant to the chief of US naval operations