NEED TO KNOW

• Vortexa tracked 34+ Iran-linked tankers crossing the blockade line since April 13
• Vessels hug Iranian, Pakistani, Indian waters where US cannot legally interdict
• China remains the primary destination as enforcement chases ships into open ocean

WASHINGTON, DC (TDR) — A US naval blockade announced as "total" three weeks ago is being routinely circumvented by Iranian oil tankers exploiting a basic feature of international maritime law.

The big picture: The blockade is real but porous, and the workaround was predictable from the legal architecture.

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• President Trump implemented the blockade April 13 under CENTCOM authority
• Maritime intelligence firm Vortexa has tracked at least 34 Iran-linked vessels transiting since
• Six confirmed outbound crude carriers moved roughly 10.7 million barrels

Why it matters: Sanctions enforcement depends on credibility. Each tanker that lands cargo unchallenged signals to oil buyers that the cordon has gaps.

• Iranian crude revenue ran roughly $5 billion last month by conservative estimate
• That figure is up roughly 40 percent over pre-war earnings
• Two VLCCs delivered to Indian ports in mid-April under a temporary US waiver since expired

Driving the news: The method is straightforward and legal under the UN Convention on the Law of the Sea.

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• Tankers switch off AIS transponders before departure, going dark to public tracking
• Vessels hug coastlines through Iranian, Pakistani, and Indian territorial waters
• Under UNCLOS innocent passage provisions, US warships cannot interdict inside another state's 12-mile zone
• Satellite imagery from Windward tracks 719 Iranian dark fleet tankers operating globally

What they're saying: The administration's posture and the data tell different stories.

• US President Donald Trump — "Tremendous success."
• CENTCOM has reported that ten merchant vessels turned back after warnings
• Chatham House analyst — the threat to interdict third-country tankers paying Iranian transit tolls "would be a very significant escalation"
• Iran's Deputy Foreign Minister Kazem Gharibabadi — "wartime conditions cannot be governed by peacetime rules"

Yes, but: The administration is not standing still on the legal limits.

• US forces boarded the Majestic X in the Indian Ocean within INDOPACOM territory
• The Pentagon has authorized global maritime enforcement, calling international waters "no refuge" for sanctioned vessels
• Interdictions have occurred near Sri Lanka, Malaysia, and the Bay of Bengal once vessels exit territorial waters

Between the lines: The legal geometry was visible before the blockade was announced. Coastal navigation under innocent passage is not a clever new evasion — it is the default loophole in any blockade short of a full quarantine, and it has been the standard Iranian sanctions-evasion playbook for years. Selling this enforcement as "total" set an expectation the legal framework cannot deliver. The expansion of interdiction authority to the open ocean is the real story: it is an admission the cordon line failed and a quiet shift toward global enforcement that risks confrontation with India, Pakistan, and China.

What's next:

• Watch whether US forces interdict a third-country flagged tanker — the Chatham House escalation threshold
• Vortexa and TankerTrackers expected to publish late-April transit data
• Iran's closure declaration keeps roughly 2,000 ships stranded in the Gulf

If a blockade can be circumvented by sailing close to shore, what is the policy actually buying — and what is the cost of pretending otherwise?

Sources

This report was compiled using maritime tracking data from Vortexa and Windward, reporting from The National, World Oil, Euronews, Al Jazeera, India TV News, Foreign Policy in Focus, and legal analysis from Chatham House, and CENTCOM statements.

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