Iran is escalating the war by attacking ships along a key oil route. Here’s what we know.

By Issy Ronald, CNN

(CNN) — Iran might be outgunned and outspent by the US and Israel, but it has one major advantage — its control over the Strait of Hormuz.

By attacking ships navigating the narrow waterway, Iran has effectively shut the route through which one-fifth of the world’s oil supply passes.

Iran’s new Supreme Leader Mojtaba Khamenei gave no sign of relenting, warning in his first purported message, that the strait will remain closed as a “tool of pressure.”

While the strait remains almost entirely closed to Western-aligned shipping traffic, Iranian oil is still passing through, according to several marine intelligence trackers, underlining Tehran’s control of it.

Here’s what you need to know:

What is Iran doing?

Iranian activity near the strait has become more aggressive as it attempts to choke off one of the global economy’s key arteries. More than a dozen vessels have been attacked since the war began.

Even in peacetime, great skill is required to navigate the strait’s narrow channel and busy traffic. Now any once crossing risks being fired on from sea or the nearby Iranian coast.

On Tuesday it emerged that Iran had begun laying mines in the strait, according to two people familiar with US intelligence on the matter.

The mining is not extensive, but Iran still maintains upward of 80% to 90% of its small boats and minelayers, one source told CNN, contradicting US President Donald Trump’s claim that Tehran has “no navy.”

Such a move underlines Iran’s reliance on asymmetric warfare and the havoc these tactics could wreak even as the country is battered by US-Israeli airstrikes.

Trump later sowed confusion about the issue, saying he didn’t think Iran had managed to lay any mines and that the US had taken out “just about all” their minelaying ships.

Iran has around 5,000 to 6,000 naval mines, a report from the US Congress estimated last year. That total includes many different types of mines, the report said. Some are limpet mines, which are usually manually attached to a ship’s hull by a diver; some are moored mines, which float just below the surface and explode when they come into contact with a ship; and some are “bottom” mines, which rest on the sea floor before detonating when they detect a nearby vessel.

Still, mines are just one part of the threat posed by Iran in the strait.

Its Islamic Revolutionary Guard Corps (IRGC), a military force that has its own navy, is still capable of deploying a “gauntlet” of mines, explosive-laden suicide boats and shore-based missile batteries, causing one US source to describe the strait as “Death Valley.”

Despite nearly two weeks of airstrikes, the IRGC’s “main small craft fleet has largely remained intact,” said Farzin Nadimi, a senior fellow at the Washington Institute who has written about Iran’s naval strategy.

How has the US responded?

Securing the strait for commercial shipping is causing another headache for the US.

Trump called on oil tanker crews to “show some guts,” and even said the US Navy provide escorts if necessary but this would put naval vessels in harm’s way with no obvious strategic advantage for the war itself.

But his administration has given mixed messages. Top US general Dan Caine refused to commit to such an operation on Tuesday, saying the US would look at a “range of options” if tasked with escorting vessels. And Energy Secretary Chris Wright noted that the navy was not yet capable of escorting vessels, and could likely only do so by the end of the month.

While it’s technically possible to create the conditions for some ships to pass through the strait within days or weeks, restoring long-term sustained security to the strait could take months, according to Nadimi, the analyst. “It cannot be done quickly and it cannot be done under enemy fire,” he said.

Even if escorts can be managed, oil tanker flows would likely remain at least 10% less than normal, according to Lloyd’s List Intelligence. That figure could be “significantly lower depending on Iran’s response,” and any potential minesweeping operations, it said.

US Central Command said Tuesday it destroyed multiple Iranian naval ships — including 16 minelayers — near the strait, though it did not mention destroying any mines.

What’s at stake?

The longer the Strait of Hormuz remains impassable, the graver the implications for the global economy.

With the strait effectively closed, 15 million barrels of crude and 5 million barrels of other oil produces remain stranded in the Gulf every day, according to the director of the International Energy Agency.

“They want to inflict pain,” Nadimi told CNN. “The strategic objective is to inflict as much punishing pain as necessary on the US military bases in the region, Israeli homeland, Persian Gulf countries, and indirectly the US homeland.”

While there are some other options for exporting crude via pipelines, the world’s biggest oil exporter, Saudi Aramco, warned on Tuesday of the potentially “catastrophic consequences” for oil markets if flows don’t resume through the strait.

Even the IEA’s announcement it had agreed to release 400 million barrels of oil into the global market – the largest such emergency release in history – did little to quell oil market volatility. And those 400 million barrels only staunch the shortfall for 26 days.

Already in Asia, which imports 60% of its oil from the Middle East, some countries are taking drastic measures to reduce their energy consumption. Schools have closed in Pakistan, South Korea is imposing a fuel price cap for the first time in 30 years, and Thailand has ordered government employees to work remotely.

Has this happened before?

Yes. During the Iran-Iraq war in the 1980s, both countries targeted each other’s oil tankers in the Persian Gulf. Iran’s navy laid mines close to the Strait of Hormuz, and one of these struck a US warship, the USS Samuel B. Roberts.

The ship suffered substantial damage, and the Reagan administration retaliated by damaging or sinking three Iranian warships and three oil platforms, drastically reducing Tehran’s ability to engage in the gulf.

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CNN’s Natasha Bertrand, Brad Lendon, Catherine Nicholls, Tim Lister and Sophie Tanno contributed to this report.