For years now, ships involved in sanctioned and illicit trade have “gone dark” to avoid detection — that is, switched off their automatic identification system (AIS) transponders to make themselves virtually invisible to authorities and other vessels.
This dark shipping practice, while not inconsequential, has largely been limited to the “shadow fleets” transporting sanctioned Iranian and Russian oil. But for energy tankers looking to sail through the fraught waters of the Strait of Hormuz, avoiding detection is increasingly becoming a necessity.
This is what has brought this risky tactic out of the margins. Here’s a look at how the conflict in West Asia has driven this response, and why this is so dangerous.
Iran war constricts Strait of Hormuz traffic
Before the war began on February 28, the Strait of Hormuz accounted for a fifth of global oil and liquefied natural gas (LNG) flows. Maritime traffic through the waterway has since reduced to a trickle amid threats, and even a few attacks on merchant vessels.
India depended heavily on the Strait of Hormuz for its energy imports, with over 40% of its oil imports, 60% of its LNG imports, and 90% of its liquefied petroleum gas (LPG) imports coming through the narrow passage that connects the Persian Gulf to the Gulf of Oman and the Arabian Sea. Many of the energy cargoes that have reached India via the Strait of Hormuz over the past three months also went dark as they crossed the strait.
Among the most recent examples was the LNG tanker Al Hamra, operated by an arm of the Abu Dhabi National Oil Company. Trade sources indicated that Al Hamra had not transmitted its location for days by turning off its transponder, before emerging again on the map on May 23 after crossing the strait. It arrived at Gujarat’s Dahej on May 26.
“What began as a behaviour largely associated with Iran-linked tonnage has broadened materially. Non-Iranian operators now account for the majority of dark outbound laden transits through the Strait (of Hormuz). AIS-off movements through Hormuz are no longer only a sanctions-evasion signal. They have become a wider commercial response to conflict risk, operational uncertainty, and the need to keep Gulf cargo moving through one of the world’s most important energy chokepoints,” said Claire Jungman, director of maritime risk & intelligence at energy and freight markets analytics firm Vortexa, in a recent note.
Surge in dark transits through Strait of Hormuz
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According to International Maritime Organization (IMO) guidelines, AIS should always be in operation when a ship is sailing or at anchor, unless the master of the ship decides that broadcasting the information is a threat to its safety or security.
AIS is seen as critical for safe maritime navigation. Switching the transponder off essentially makes the vessel untrackable and invisible to other ships’ systems, which can significantly increase the risk of collisions at sea. This risk becomes even greater in crowded waterways such as the Strait of Hormuz.
According to Vortexa data, dark transits through the Strait of Hormuz — between March 1 and late May — represent 57% of all transits recorded over the period.
This trend of ships going dark while transiting the strait has intensified in recent weeks. The share of outbound laden vessels transiting dark stood at 58.5% in March, slightly dipped to 54% in April when vessel movements through the waterway picked up slightly through corridors regulated by Iran, and then rose sharply to 65.2% in May, as per Vortexa.
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“Commercial operators are simultaneously adapting both operationally and physically to the environment through prolonged dark operations, altered routing, escort behavior, and possible vessel hardening measures. Taken together, the Strait of Hormuz is increasingly functioning as a contested low-visibility operating environment where commercial transit continues, but under growing military pressure, degraded transparency, and sustained enforcement risk,” maritime intelligence provider Windward said in a note last month.
Of the energy cargoes being transported by tankers that are going dark to cross the Strait of Hormuz, crude oil and condensates account for around 40%, ‘clean products’ (like petrol, diesel, jet fuel, and naphtha) account for about 25%, ‘dirty products’ (like bunker oil and bitumen) have a share of about 18%, and LPG accounts for about 14%, shows Vortexa data. LNG tankers, which hitherto were absent from dark shipping activity in the region, appear in the data from April into May.
“…the deterioration in visibility is not limited to crude or sanctioned flows. That matters because the market impact is broader than crude balances alone. When clean products, LPG, and LNG also move with reduced AIS visibility, the uncertainty extends into refinery supply, product availability, regional inventories, and destination-level demand reads,” Jungman said.
Sailing dark now an accepted operating protocol
This behaviour is no more limited to shady shippers or vessels carrying sanctioned cargo from Iran.
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Ship tracking data shows that tankers belonging to or chartered by the national energy companies of countries such as the UAE, Qatar and Saudi Arabia are also going dark to cross the strait. In March, non-Iranian operators accounted for 37% of dark outbound laden transits through the chokepoint, which rose to 56% in April and 67% in May.
According to Jungman, the shift suggests AIS-off behaviour is becoming an accepted operating protocol, not an exceptional measure. Iran-linked vessels helped establish the template before and during the early phase of the crisis. Non-sanctioned Gulf tonnage is now increasingly using similar methods — and, in volume terms, beginning to dominate them.
Vortexa analysis shows that UAE-linked vessels account for the largest share of dark transits at around 27%, followed by Iraq at about 11%, and Qatar at around 10%. Saudi Arabia, Kuwait, and Bahrain together account for another 9%. “This means dark activity through Hormuz can no longer be treated as a proxy for Iranian or sanctioned flows. That framing no longer holds,” Jungman said.
Experts point out that with global energy flows disrupted due to the crisis, there is increasing pressure on the major energy producers from the Gulf to keep exports going to the extent possible. Most of these countries depend heavily on the revenue they earn from energy exports, and the shipping disruption in the Strait of Hormuz has already hurt them from a macroeconomic standpoint. Some of them also took hits on critical energy infrastructure from Iran in the first few weeks of the war.
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“The UAE departures chart makes the scale of this shift explicit. Overall departures from UAE have remained substantial throughout the crisis, but the share of those loads occurring dark has risen from negligible levels in early March to above 90% in the most recent weeks. The export system is adapting, not stopping — with more cargo moving through channels where the loading event is harder to observe through AIS,” Jungman said.
