Roughly 20% of the world’s oil consumption, or about 17 million barrels per day, passes through the Strait of Hormuz. At its narrowest point, the Strait is about 33 kilometres wide, but shipping is confined to designated lanes that function like highways at sea.

Each lane is approximately three kilometres wide, with one for inbound traffic and one for outbound traffic, separated by a buffer zone. Large oil tankers, some carrying over two million barrels of crude, are therefore funnelled into narrow, predictable corridors where movement is visible and difficult to alter.

In practice, a waterway is not open simply because ships can pass through it. It is open when operators are willing to accept the risk. That decision is determined by insurers, who price the probability of loss.

Commercial vessels are required to carry insurance before they can operate. This includes cover for the ship, the cargo, and liability for environmental damage. When a route is classified as high risk due to conflict, insurers impose a war-risk premium, an additional charge that reflects the danger of operating in a conflict zone. Under normal conditions, this premium can be as low as 0.05% of a vessel’s value, but in periods of conflict, it can rise to between 0.5% and 1% or more per voyage.

For a large oil tanker valued at around $100 million, this means the cost of insurance can increase from roughly $50 000 to over $1 million per trip. After major incidents, premiums can rise even further, or insurers may withdraw coverage entirely. When that happens, ships stop moving, regardless of naval protection.

The United States (US) and its allies retain significant naval capabilities in the region and may be able to protect vessels in transit. Yet the ability to escort ships is not the same as restoring normal commercial traffic.

The Strait itself increases exposure. Ships must follow fixed lanes, making their position, speed, and timing predictable. Unlike in open ocean, they have limited room to manoeuvre.

Iran does not need to control the Strait to disrupt it. It can rely on a layered threat environment that includes naval mines, drones, and anti-ship missiles.

Naval mines are particularly effective. Many are compact devices positioned just below the surface or anchored to the seabed, designed to detonate when a vessel passes nearby. A typical mine can carry 100 to 300 kilogrammes of explosive, enough to tear open the hull of a large ship.

These devices can remain in the water for days or weeks and are difficult to detect. If triggered beneath a tanker weighing over 100 000 tonnes, the explosion occurs below the waterline, forcing water into the hull and damaging internal structures. Even a single detonation can disable propulsion or flood sections of the vessel.

Once a mine strike occurs, the surrounding area is treated as contaminated. Traffic slows or stops while specialised vessels conduct clearance operations using sonar and remote systems. Clearing even a small number of mines can take days or weeks.

Escort operations do not remove that uncertainty and also concentrate risk. Instead of ships moving independently, traffic is compressed into tight formations that are easier to track and target.

The consequences of a single successful strike in this setting would extend well beyond the vessel that is hit as this would demonstrate that naval protection does not eliminate exposure, prompting insurers to reassess the entire route.

The impact would be greater still if a US or allied warship were damaged or sunk while conducting escort operations. Beyond the operational loss, such an event would carry significant political consequences. The loss of a warship, particularly with casualties, would likely trigger strong domestic reactions and increase pressure on governments to reconsider their involvement.

This dynamic affects decision-making before any incident occurs. Escort operations carry not only military risk, but political risk. The potential for escalation, combined with the domestic consequences of losses, helps explain why such missions are approached with caution.

From late 2023 into 2024, Western navies, led by the US under Operation Prosperity Guardian, deployed sustained escort operations in the Red Sea in response to repeated drone and missile attacks by Houthi forces targeting commercial shipping. US and allied warships intercepted dozens of incoming threats using advanced air defence systems, while maintaining a continuous presence along key shipping routes.

Despite this, major shipping companies, including some of the world’s largest container operators, began rerouting vessels around the Cape of Good Hope. This added approximately 10 to 14 days to journeys between Asia and Europe and significantly increased fuel and operating costs. Traffic through the Suez Canal declined sharply as insurers raised war-risk premiums and operators chose to avoid the route.

The Strait of Hormuz presents a more concentrated version of the same problem. It carries a larger share of global energy trade, operates within a narrower space, and sits within range of multiple overlapping threats. Even limited incidents can shift how the entire route is priced.

The Strait is not opened by warships. It is opened when risk is priced low enough for ships to return.