The Strait of Hormuz is once again the scene of fighting, with Iran and the United States States vying for control of the strategic waterway and continuing to trade fire in the early hours of Thursday.
When the US and Israel launched the war on Iran on 28 February, Tehran effectively closed the strait to shipping traffic.
That move sent the price of oil, fertilizer and many other goods soaring far beyond the region and gave Iran major leverage in negotiations.
So how do the countries directly involved in the conflict — and the international community —know what's happening in this vast stretch of water?
"There's no one monitoring authority," explains Commodore Steve Prest, a retired naval officer and Associate Fellow at Royal United Services Institute (RUSI).
