France, May 2 -- Since the start of the Iran war in late February, staff at a maritime security centre in western France have been helping merchant ships trapped in the Gulf.

Twin Iranian and US blockades of the Strait of Hormuz have left more than 750 civilian ships stranded on the Gulf side of the passageway, through which a fifth of global crude oil and liquefied natural gas transited before the conflict. Only a handful have managed to leave in recent weeks.

If the Maritime Information Cooperation and Awareness Centre (MICA centre) detects any form of bombardment, it immediately sends nearby ships - container ships, cargo vessels and cruise liners - an encrypted message. Commanding officer Thomas Scalabre oversees the monitoring

"We...