Somewhere in the Gulf of Oman in early 2025, a Chinese anti-submarine warfare frigate fell into formation alongside Russian and Iranian warships, and the three navies began hunting for submarines together. The exercise was not a first. It was the latest iteration of a series called “Maritime Security Belt” that has run annually since 2019, each round growing more ambitious and drawing more spectators. This time, the drill zone stretched across roughly 17,000 square kilometers of water that sits just south of the Strait of Hormuz, the narrow passage through which the U.S. Energy Information Administration estimates about 21 percent of the world’s petroleum supply flows every day.
Five countries sent military observers: Azerbaijan, Kazakhstan, Oman, Pakistan, and South Africa. The presence of Oman and Pakistan stood out. Both maintain defense ties with Washington. Both chose to watch three of America’s chief strategic rivals rehearse tactics designed, at least in part, to complicate the operations of U.S. submarines and carrier strike groups that patrol the same waters.
What happened during the drills
Russian and Chinese warships entered Iranian territorial waters specifically to participate. Official footage released by Tehran showed coordinated surface maneuvers, gunnery practice, helicopter sorties, and formation sailing across the exercise box. Iranian state media and military spokespeople framed the drills as contributions to regional security, anti-piracy cooperation, and protection of commercial shipping. Moscow and Beijing echoed those themes, calling the exercises defensive and routine.
But the centerpiece was anti-submarine warfare. The three navies practiced search patterns and coordinated surface-ship movements consistent with tracking and prosecuting undersea targets. China’s participation with a frigate configured for ASW work was particularly notable. Beijing operates several modern frigate classes optimized for towed-array sonar and embarked anti-submarine helicopters, including the widely exported Type 054A. While no official Chinese defense ministry statement has confirmed the exact hull or sensor suite deployed to the Gulf of Oman, the exercise’s stated focus on submarine hunting and the vessel’s reported role align with the capabilities of that class.
The geographic choice sharpened the signal. The Gulf of Oman is not a remote training range. It is the immediate approach to the Strait of Hormuz, where the U.S. Fifth Fleet, headquartered in Bahrain, maintains a near-constant presence. In 2024 and early 2025, U.S. carrier strike groups including the USS Abraham Lincoln and USS Harry S. Truman operated in and around the Arabian Sea and Gulf of Oman. Any coordinated anti-submarine capability tested in those waters has direct implications for American submarines transiting the strait and for the screening forces that protect carrier groups.
Why repetition matters more than any single drill
A one-off exercise can be dismissed as political theater. The Maritime Security Belt series is no longer a one-off. Reporting confirms the drills continued into 2025 as a new iteration, again near the Strait of Hormuz, while tensions between Tehran and Washington over Iran’s nuclear program and regional proxy conflicts remained high.
Navies that train together repeatedly develop something that single exercises cannot produce: interoperability. Shared communications protocols, compatible data formats, tactical trust between bridge crews who have watched each other maneuver under pressure. Each cycle gives the three fleets another opportunity to refine how they hand off a sonar contact from one ship to another, how they coordinate helicopter search grids, and how they deconflict weapons-release zones. Whether they have crossed the threshold from parallel operations to genuinely fused anti-submarine warfare is an open question, but the trajectory is clear, and each year of practice shortens the time they would need to adapt in a real crisis.
Iran’s own submarine fleet adds another layer. Tehran operates Russian-built Kilo-class diesel-electric submarines, domestically produced Fateh-class boats, and a fleet of Ghadir-class midget submarines designed for shallow-water operations in and around the strait. If Iran’s partners are practicing how to find and track submarines in these waters, they are also, implicitly, learning the acoustic environment that Iran’s own boats would exploit in a conflict. The knowledge cuts both ways.
What remains genuinely unclear
Several important details have not been disclosed by any participant. No primary defense ministry record has specified the anti-submarine tactics practiced, whether live torpedo firings or depth-charge drops occurred, or whether the three navies achieved integrated command-and-control capable of fusing sonar tracks from Russian, Chinese, and Iranian sensors into a single undersea picture. That kind of data-sharing is technologically and politically complex. Without access to exercise orders or communications logs, outside analysts cannot say whether the three navies merely sailed in proximity or actually practiced the tightly coupled coordination required to threaten a modern, quiet submarine.
The Pentagon has not publicly released an assessment of the exercises. U.S. Central Command has not commented on the proximity of the trilateral drills to American assets, and no authoritative public map has shown the exact distance between the exercise box and any U.S. submarine or carrier in the area. That silence could mean Washington views the drills as low-grade posturing. It could also mean the response is unfolding through classified channels, adjusted patrol patterns, or intensified exercises with Gulf partners. Neither interpretation can be confirmed from open reporting as of June 2026.
The five observer nations have not published their own after-action assessments. Whether their delegations watched live tactical phases or only attended ceremonial openings and closings is unknown. The distinction matters: observation of real-time ASW operations would represent a far deeper level of military transparency than a scripted port visit.
What this means for the Strait of Hormuz
The practical question for energy markets, regional governments, and the U.S. Navy is straightforward: can Iran, Russia, and China now credibly threaten to slow or complicate American submarine and carrier operations in the Gulf of Oman?
Based on available evidence, the answer is not yet. The three navies are not in a position to deny access outright to the world’s most capable undersea force. But they are steadily improving their ability to monitor, track, and potentially harass foreign naval movements near the strait. They are investing real ship-days, fuel, and diplomatic capital in building a combined anti-submarine capability in the one place where it would matter most.
The underwater domain around one of the world’s key energy arteries is getting more crowded, more contested, and less forgiving of miscalculation. Each iteration of the Maritime Security Belt drills narrows the gap between a coalition on paper and a coalition that could complicate American operational planning in a crisis. That gap has not closed. But it is closing, and the three navies are making sure the world is watching.
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*This article was researched with the help of AI, with human editors creating the final content.
