Maritime Terms Explained: The Iran War & Strait of Hormuz Crisis

Four weeks into the Iran war, maritime traffic through the Strait of Hormuz has not ceased, but it has fundamentally changed. AIS-visible crossings dropped to near zero at multiple points, with only 16 vessels recorded transiting the Strait throughout the third week of the conflict. Despite this collapse in visible movement, oil exports have continued, cargo flows remain active, and vessels are still operating across the Gulf and beyond. The system has not broken, but has shifted into a constrained and controlled operating environment.

This transition is not being driven by a single factor. It reflects the combined effect of restricted access, altered routing behavior, degraded visibility, insurance pressure, and adaptive trade mechanisms. As a result, understanding the current maritime picture requires understanding the terminology that now defines how the system functions: AIS behavior, dark activity, war risk exposure, vessel classes, and alternative routing structures.

Most of these terms appear frequently in reporting but are rarely explained in context. The current crisis makes that gap more consequential. The Strait of Hormuz is not only a geographic chokepoint — it is a system where physical constraints, legal frameworks, financial mechanisms, and operational behavior intersect. Each of the terms below reflects one part of that system and explains how maritime activity continues under conditions that are materially different from normal operations.

The Geography

The Strait of Hormuz is one of the most critical maritime chokepoints in the global trading system. A maritime chokepoint is defined by a narrow passage through which a large share of global shipping must pass, creating structural vulnerability to disruption. Located between Iran to the north and Oman and the United Arab Emirates to the south, the strait connects the Arabian Gulf (also known as the Persian Gulf and the Middle East Gulf) to the Gulf of Oman and the Arabian Sea, forming the primary gateway between Gulf energy exporters and global markets.

Under normal conditions, Hormuz facilitates roughly 20% of global oil and gas flows, with approximately 20 million barrels transiting the corridor each day. This concentration of volume within a geographically constrained route means that even limited disruption can quickly affect energy markets, shipping behavior, and maritime risk calculations.

While the Strait is effectively closed, the reality on the water is more nuanced. Transit has not stopped entirely, but it has shifted away from open, unrestricted passage toward tightly controlled access. Vessels are still moving, but increasingly through routes that run along Iranian territorial waters rather than standard international navigation lanes. This reflects a shift from unrestricted passage to a selective transit model in which access appears contingent on cargo type, destination, and alignment with Iranian interests.

The effect of disruption at Hormuz extends beyond the immediate region. The Bab el-Mandeb Strait, another critical chokepoint that connects the Red Sea to the Indian Ocean and serves as a key gateway to the Suez Canal, has shown sharp volatility as operators test and reassess exposure to regional risk. Traffic initially dropped to minimal levels before rebounding, reflecting short-term utilization rather than sustained confidence in the corridor. Bulk carriers and general cargo vessels led these movements, indicating broader commercial repositioning under uncertainty.

At the same time, traffic around the Cape of Good Hope at the southern tip of Africa has remained elevated, signaling a sustained shift toward longer, more stable routes that bypass both the Gulf and Red Sea threat environments. These diversions are being driven by mainstream commercial operators, not just high-risk activity, reinforcing that rerouting is becoming a structural response rather than a temporary adjustment.

Taken together, these patterns show a system redistributing risk across multiple chokepoints, with routing decisions increasingly shaped by security conditions rather than efficiency.

Saudi Arabia’s Petroline, the East-West pipeline built in the 1980s, spans approximately 1,200 kilometers and connects Gulf production to Red Sea export terminals. In the current environment, it has become increasingly important by enabling crude to reach Yanbu without transiting Hormuz, providing a structural alternative that partially mitigates chokepoint dependency. This is not a replacement for the Strait, but a redistribution mechanism that allows key volumes to bypass the most constrained corridor. 

By March 22, more than 30 tankers were present at Yanbu port and anchorage, while 64 crude tankers were signaling Yanbu as their destination, reinforcing the Red Sea corridor as a primary alternative to Hormuz transit.

The Ships

Maritime awareness depends heavily on AIS, the Automatic Identification System used by vessels to broadcast identity, position, speed, and destination. As a self-reported signal transmitted via onboard transponders, AIS is widely accessible and foundational to vessel tracking. 

Originally designed for navigation safety, not security or enforcement, AIS relies on cooperative reporting, meaning that data can be incomplete, misleading, or deliberately manipulated. These limitations predate the Iran conflict and are built into how the system operates. Vessels may disable or alter AIS for a range of reasons, from operational safety to deliberate concealment tied to sanctions evasion, smuggling, or other illicit activity. As a result, AIS provides visibility, but not certainty, and its reliability as a standalone source is inherently limited.

That limitation is reflected in the rise of dark activity. Going dark refers to vessels disabling AIS transmissions, removing themselves from conventional tracking systems, often in high-risk or sensitive areas. In the current conflict, dark activity across the Gulf reached 427 events on March 20, in addition to vessels operating without AIS transmission near the Strait of Hormuz. 

In one case, a vessel associated with sanctioned networks stopped transmitting near Khor Fakkan before reappearing inside the Gulf, consistent with ballast movement and concealed transit behavior. 

While AIS gaps can occur for benign reasons, their context, duration, and associated behavior determine risk. Remote Sensing Intelligence, including SAR, EO, and RF data, is used to verify vessel presence during these gaps, confirming whether ships are experiencing signal loss or deliberately concealing movement. This ensures that the absence of AIS signals is not misinterpreted as the absence of activity.

In parallel, AIS is being used in a more deliberate and strategic manner. Defensive AIS messaging has emerged as vessels actively broadcast identity signals, including crew nationality and ownership, that appear intended to communicate compliance or reduce targeting risk during transit. This represents a shift from AIS as a passive reporting system to an active signaling mechanism within a constrained operating environment.

This behavior is visible in the Strait. Windward identified 36 vessels broadcasting nationality signals through AIS destination fields, a pattern that emerged during the second week of the conflict. Of these, 23 were Chinese-linked vessels transmitting standardized messages such as “CHINESE CREW OWNER” and “CHINA OWNER & CREW.” Additional signals included Iraqi-linked vessels broadcasting “IRAQI OWNER” and a Turkish vessel indicating “TURKISH CREW.” 

These transmissions appear designed to signal alignment or neutrality, reinforcing that access through Hormuz is no longer only navigational, but increasingly conditional.

At the same time, even as vessels are using AIS more deliberately to signal identity and reduce risk, the reliability of those signals is being undermined by the operating environment itself.

GPS jamming is the deliberate interference with satellite navigation signals, disrupting a vessel’s ability to determine and broadcast its true position. Because AIS depends on GPS inputs, this interference directly affects how vessels appear on tracking systems.

In the current conflict, the electronic environment across Gulf shipping lanes has degraded sharply. Within the first 24 hours following the launch of Operation Epic Fury, Windward detected more than 1,100 vessels impacted by GPS and AIS interference.

AIS signals were displaced into impossible locations, including UAE airports, the Barakah nuclear facility, inland areas of Iran, and circular “crop-pattern” distortions across Gulf waters, making vessels appear where they physically were not.

During the second week of the conflict, Windward identified more than 30 jamming clusters across Saudi Arabia, Kuwait, the UAE, Qatar, Oman, and Iran, highlighting that this is not isolated interference but a widespread and sustained disruption to maritime positioning systems.

Vessel scale is a critical part of understanding impact. VLCCs, or Very Large Crude Carriers, are among the largest tankers in operation, capable of transporting approximately two million barrels of oil in a single voyage. In the current environment, disruptions affecting even a small number of these vessels can materially influence global supply flows, pricing expectations, and downstream energy markets.

Taken together, these patterns show that vessel visibility in the current conflict is not a stable foundation for maritime awareness. In and around the Strait of Hormuz, AIS signals can be missing, manipulated, or deliberately broadcast to signal compliance, while GPS interference distorts how vessels appear across the region. The result is a fragmented and conditional operating picture, where presence, identity, and intent cannot be inferred from AIS alone, and where understanding real activity requires continuous validation across multiple intelligence sources.

The Money

Financial mechanisms play a central role in shaping maritime behavior under conflict conditions, often determining whether vessels move at all. War risk insurance is required for vessels operating in high-risk areas and reflects the perceived threat environment. As risk increases, premiums rise, coverage becomes more restrictive, and in some cases, insurers may decline to provide or withdraw coverage entirely. 

This dynamic was visible immediately after the escalation of the conflict. Traffic through the Strait of Hormuz declined by approximately 80% within 24 hours, as shipowners and charterers reassessed whether voyages could proceed. By March 3, only four vessels crossed the Strait, down from a seven-day average of roughly 77, reflecting not only physical risk, but financial and insurance constraints.

Protection and indemnity clubs (P&I Clubs) — the mutual insurers that cover third-party liabilities for roughly 90% of the global merchant fleet — are a critical component of this system. Without P&I coverage, vessels cannot operate commercially at scale, as exposure to third-party liabilities becomes unmanageable. In high-risk environments, the interaction between war risk insurers and P&I Clubs determines whether vessels can transit and under what conditions.

Following the escalation, major P&I Clubs issued 72-hour cancellation notices on war risk extensions for vessels operating in the region, triggered by the withdrawal of reinsurance support. Without these extensions, vessels are exposed to liabilities arising from war-related incidents, making commercial operations effectively unviable.

The withdrawal of reinsurance reflects aggregation risk, as hundreds of vessels cluster in a confined area under escalating threat conditions. As a result, even when transit remains physically possible, voyages often do not proceed. Without insurance, vessels cannot be chartered, and cargoes cannot be financed.

The Joint War Committee (JWC) formalizes this risk environment through the designation of Listed Areas. In the current conflict, this designation has expanded materially. On March 3, the JWC added Bahrain, Djibouti, Kuwait, Oman, and Qatar, while broadening the defined risk boundaries across the Persian/Arabian Gulf, Gulf of Oman, and adjacent Indian Ocean and Red Sea corridors.

These updates reflect a widening perception of risk beyond a single chokepoint to an entire regional operating environment. The expansion of high-risk zones across the Gulf has been accompanied by a sharp increase in war risk premiums, rising from approximately 0.2% to as much as 1% of vessel value per voyage, with some underwriters declining to quote new coverage altogether. In practice, this shifts routing decisions from purely operational considerations to financial viability, reinforcing that access to Hormuz is increasingly determined by insurability rather than physical navigability.

Force majeure clauses further illustrate how contractual frameworks respond to disruption. As transit becomes unreliable or infrastructure is affected, contractual obligations can be suspended, allowing parties to avoid penalties under extraordinary circumstances. In the current environment, the constrained transit, infrastructure disruption, and rerouting behavior create conditions where force majeure becomes operationally relevant.

Despite these constraints, flows continue due to policy intervention and cargo already in motion. The issuance of OFAC General License 134 enabled the completion of deliveries for Russian-origin crude loaded prior to March 12, covering approximately 215 million barrels across 377 tankers. 

At the same time, General License U allows Iranian crude already on the water to be sold through April 19, with approximately 163 million barrels currently in transit, primarily toward China, receiving over 90% of Iranian crude exports.

As a result, the system remains active, but under fundamentally different conditions. Movement is no longer driven purely by market demand, but by a combination of insurance availability, regulatory allowances, and risk tolerance, with financial mechanisms effectively determining when and how maritime access is possible.

The Evasion

The persistence of maritime flows under restrictive conditions reflects how quickly the system adapts under pressure. The shadow fleet, often referred to as the dark fleet, consists of vessels that rely on deceptive shipping practices to move sanctioned or high-risk commodities while concealing their true origin, ownership, or destination. This ecosystem expanded rapidly following earlier sanctions regimes and is now actively exploiting the current conflict environment.

These vessels operate through multiple layers of obfuscation. AIS suppression is one method, but identity manipulation plays an equally important role. Zombie vessels, which operate under the identity of defunct or scrapped ships, demonstrate how vessel identity itself can be repurposed to enable movement. 

In one case during the conflict, a 26-year-old LNG carrier transited the Strait on March 20 before going dark. Its IMO number corresponded to a vessel listed as “broken up” in the Equasis database, with its first signal in the region appearing days earlier, despite records indicating it had been sent for scrapping months prior.

This reflects how the shadow fleet is exploiting reduced visibility and selective transit conditions in the current conflict, using recycled identities to operate alongside legitimate traffic with lower scrutiny.

Ship-to-ship (STS) transfers involve the movement of cargo between vessels at sea, often used to obscure the true origin, destination, or ownership of a shipment. During the second week of the war, the sanctioned Russian tanker M/V TRUST conducted a high-probability semi-dark transfer in Omani waters involving approximately 325,000 barrels of crude, temporarily disabling AIS during a prolonged rendezvous before resuming transmission. 

The timing of the operation suggests that reduced visibility across the Gulf is being used to facilitate illicit cargo movements.

Flagging practices further contribute to this opacity. Vessels may shift registries, operate under flags of convenience, or adopt false identities to reduce scrutiny and regulatory exposure. In parallel, falsely flagged vessels have transited the Strait while signaling destinations such as China, reinforcing that access is being granted under specific operational and political conditions.

Together, these behaviors show how the current conflict environment is enabling deceptive shipping practices to scale with legitimate trade flows. Reduced visibility, controlled transit, and shifting enforcement priorities are not just constraints — they are conditions that allow shadow fleet operators to embed themselves within legitimate flows and move sanctioned cargo.

The Law

Maritime operations are governed by international legal frameworks, most notably the United Nations Convention on the Law of the Sea (UNCLOS), which established the legal structure for how oceans are used and navigated. Among its provisions is the right of transit passage through international straits such as Hormuz, meaning vessels should be able to move through the Strait without interference.

In practice, the current situation demonstrates the limits of legal frameworks under geopolitical pressure. While the legal right to transit remains in place, operational access is being shaped by control over routing, selective authorization, and elevated threat conditions, including at least 20 vessels targeted or attacked by IRGC-linked activity since the start of the conflict.

Organizations such as the United Kingdom Maritime Trade Operations (UKMTO) provide real-time security alerts and act as a central coordination point for vessels operating in high-risk areas, supporting mariners with verified threat information and incident reporting across contested environments.

Maritime Security (MARSEC) levels define the security posture across maritime domains,  providing a standardized framework to scale protective measures based on threat severity, from routine operations to imminent or active incidents. In the current environment, these mechanisms help translate evolving risk into operational decisions, even as conditions on the water continue to shift rapidly.

These frameworks remain relevant, but they do not determine outcomes independently. The interaction between law, enforcement, and operational control defines how the system functions in practice.

The current situation also echoes elements of what is historically referred to as a tanker war, where commercial shipping becomes a direct or indirect target within a broader conflict. While the scale and form differ, the targeting of vessels, constrained transit, and insurance-driven disruption reflect a similar dynamic, where maritime trade is not only affected by conflict but becomes part of the operational environment itself.

The Bypass

As transit through the Strait of Hormuz became constrained, alternative routes and infrastructure shifted from optional to essential.

Saudi Arabia’s Petroline, the East-West pipeline built in the 1980s, spans approximately 1,200 kilometers and connects Gulf production directly to Red Sea export terminals. In the current environment, it has become a critical pressure valve, allowing crude to reach Yanbu without entering the Strait. This does not replace Hormuz, but it redistributes flows away from the most constrained corridor.

That shift is visible at scale. By March 22, more than 30 tankers were present at Yanbu, while 64 crude tankers were signaling the port as their destination. Charter rates for these voyages have surged as high as $460,000 per day, reflecting both limited vessel availability and elevated security risk across alternative routes.

This is not simply a rerouting decision. It reflects a structural shift in how supply is being maintained under constraint, with Red Sea exports scaling rapidly to support Asian demand while bypassing Hormuz entirely.

Iran is pursuing a parallel strategy. The Kooh Mobarak terminal, located east of the Strait, has emerged as an alternative export point that avoids Hormuz transit altogether. This shift is supported by the Goreh-Jask pipeline, which connects inland production directly to export infrastructure outside the Strait, reducing reliance on the chokepoint. 

On March 8, a sanctioned VLCC departed the terminal carrying approximately 1.77 million barrels of crude bound for China, with a 15+ day AIS blackout following departure. This marks the first recorded export from Kooh Mobarak in 2026, following only a single shipment in 2025, indicating historically minimal usage of the terminal.

Remote Sensing Intelligence confirmed the vessel’s presence prior to departure, reinforcing the use of both alternative infrastructure and reduced visibility to sustain flows.

While still limited in volume, this activity signals a deliberate effort to diversify export pathways and reduce dependency on contested maritime corridors.

At the same time, global shipping is adjusting at a system level. Traffic around the Cape of Good Hope has remained consistently elevated, with daily transits far above historical norms as operators commit to longer but more stable routes around southern Africa. Movements through Bab el-Mandeb and the Suez Canal have fluctuated, reflecting ongoing recalibration as vessels balance shorter routes against persistent Red Sea risk.

Taken together, these patterns show that maritime trade is not stopping, but redistributing. When chokepoints become constrained, flows shift across pipelines, alternative ports, and longer sea routes, creating a more complex and less efficient global shipping network.

Key Maritime Terms Behind the Disruption