The blockade's most effective enforcement mechanism is not the U.S. Navy. It is the insurance market. War risk premiums for commercial vessels transiting the Strait of Hormuz have surged to 35 to 50 times their pre-war levels, a repricing so severe that for many shippers, the math of a Gulf transit no longer works. [1]

Before the conflict, war risk coverage for a Hormuz passage ran between 0.02 and 0.05 percent of a vessel's insured value. Today, underwriters who are still willing to quote — and many are not — are charging 1 to 2.5 percent. For a tanker valued at $120 million, that is $1.2 million to $3 million in additional premium for a single voyage. Lloyd's of London shortened its quote validity from 48 to 24 hours, a signal that even the price of today's risk may not hold tomorrow. [1]

Lloyd's List reported that commercial shipping through the strait "immediately halted" once the blockade was announced, not because the Navy turned ships away but because insurers pulled coverage. [1] A ship without war risk insurance cannot legally carry cargo for most charterers. The approximately 800 vessels that stopped moving on Monday stopped voluntarily — stranded by actuarial tables, not by destroyers.

On X, maritime analyst Shanaka Perera has been making this argument for weeks: you do not need to close a strait. [2] You just need to make it uninsurable. Monday proved him right. The blockade enforces itself through cost, and cost is a weapon that requires no Rules of Engagement.

-- DARA OSEI, London