Naval mining: the Strait of Hormuz and Taiwan

A Conversation with Scott Savitz

Today, I’m delighted to host Dr. Scott Savitz of RAND, who is generously sharing his expertise on naval mining. I’ve asked Scott to talk through naval mining fundamentals, Iran’s mining capabilities, and ways to bolster Taiwan’s mine-laying capabilities. As with all authors at the China-Russia Report (CRR), Scott’s comments reflect his own personal opinions.

Naval Mining 101

CRR: Let’s start with the fundamentals. What are the basic categories of naval mines, how deep do they sit in the water, how expensive are they relative to commercial and military ships, can mines be laid from shore, etc?

Scott Savitz: Naval mines can be categorized in two broad ways. The first is in terms of where they sit in the water column: moored mines have buoyant cases that are tethered to an anchor on the seabed, bottom mines sit directly on the seabed, and drifting mines move with the currents. The second is what causes them to detonate. Contact mines detonate when a ship collides with them, while influence mines respond to the characteristic signatures of a ship in their vicinity, such as a ship’s magnetism, the sounds it generates, and the pressure drop it creates. Most contact mines are moored or drifting, and moored contact mines are the classic “spiky balls” that most people envision when they think of mines, while most influence mines are bottom mines.

Mines can be laid from ships and boats of all sizes, submarines, aircraft, and in select cases, even by waders. Ostensibly civilian ships can shove mines overboard when no one is looking. Mines are very inexpensive weapons compared with most military hardware, since they don’t need to propel themselves or have guidance systems. They’re very simple, but very effective. A mine costing in the low tens of thousands of dollars can incapacitate or even sink a ship costing hundreds of millions. We saw examples of this during the conflicts in the Persian Gulf during the 1980s and 1990s.

Naval Mining as a System, Not a Weapon

CRR: In a RAND analysis, How to Succeed in Deterring an Invasion of Taiwan Without Really Trying (Hard), you wrote that naval mines are “consummate operational disruptors.” What does that mean, and how do minefields interact with other capabilities, such as anti-ship missiles; shore-based artillery; Intelligence, Surveillance, and Reconnaissance (ISR); speed boats; and Global Navigation Satellite System (GNSS) spoofing to enhance systems’ lethality?

Scott Savitz: Mines create a cornucopia of problems for those trying to transit and operate in potentially mined waters. They may not know that the minefield exists or what its boundaries are, let alone the number and types of mines present. For example, all three U.S. warships that were damaged by mines in the Persian Gulf from 1988-1991 had no idea they were in minefields until mines detonated beneath them. Mine countermeasures (MCM) operations are slow and painstaking, frustrating the rest of the fleet as it waits to enter the mined area. MCM assets move slowly in predictable patterns with few defensive capabilities of their own, making them easy targets, and they’re generally designed for low signatures rather than durability. Mine clearance is often incomplete, and there is always uncertainty about the extent of residual risk, aside from the tough judgments about whether it has been reduced to an acceptable level. After all the delays associated with MCM, the fleet has to slowly transit a cleared lane, making its movements predictable while diminishing ships’ ability to maneuver in response to other threats. Mines have powerful synergies with other weapons that can take advantage of these vulnerabilities.

In a famous case, during World War I, a British-French fleet was stymied by a combination of naval minefields and artillery ashore. The MCM ships couldn’t precede the fleet into the Turkish Straits because of the artillery, and the rest of the fleet couldn’t approach the artillery to attack it because of the minefields.

ISR and environmental knowledge are critically important in mine warfare: knowing as much as possible about the adversary’s minelaying capabilities and activities, as well as the physical environment. Having a rough idea of what types of mines may be present, potential numbers that could be or have been laid, and rough areas where they may have been laid can improve the effectiveness and timeliness of MCM. It’s also important to know depth profiles, local currents, tides, and the character of the seabed (e.g., rocky or muddy). In your own waters, it’s good to do periodic scans that reveal what objects were previously on the seafloor, so that it’s easier to distinguish freshly laid mines.

Electronic warfare that reduces the accuracy of satellite navigation can disrupt MCM efforts that depend on accurate positional data, and after MCM is over, can cause ships to stumble into uncleared areas.

Iran’s Mine-Laying Capabilities and Intent in the Strait of Hormuz

CRR: You were in Bahrain supporting the U.S. Navy from 2001–2003, so you have an intimate knowledge of the Persian Gulf naval mine threat. How would you assess Iran’s current mine-laying capabilities, not only in terms of the mines themselves, but also as part of a comprehensive system? And what can the U.S., allies, and partners do to disrupt the Iranian mine-laying kill chain, either politically or militarily?

Scott Savitz: Iran has been an expert user of mines since the 1980s, with extensive experience and recognition of how effective mines can be.

The best type of MCM involves preventing mines from getting wet, as the U.S. did when it interdicted an Iranian minelayer in 1988 and an Iraqi minelayer in 2003. It’s advantageous to target mine storage depots, vehicles moving mines to loading sites, the actual loading of mines onto minelaying platforms, and the minelayers themselves (which can also be seized). However, it’s hard to stop all the mines all the time, especially since there are so many ways to lay mines, and the only signature is a splash.

Once mines are laid, there are two main approaches to MCM: hunting and sweeping. Hunting entails searching for individual mines, typically using sonar, and then neutralizing them; it’s thorough, but really time-consuming. Sweeping involves dragging gear through the water to simulate the signatures of target ships, causing mines to detonate prematurely. It’s faster (though still not that fast), but can leave some residual mine risk if the mines are able to distinguish sweeps from ships, or are using counter-countermeasures, such as detonating only after sensing signatures multiple times.

MCM and shipping delays in the Strait of Hormuz

CRR: You’ve written before on how “[m]ines can help to negate the superior power of enemy fleets not only by directly damaging their ships, but by inducing them to avoid key waters or to engage in mine-countermeasures efforts that delay and disrupt their plans.” If Iran attempted to mine the Strait of Hormuz tomorrow, what would the likely outcome be? And if Iran successfully laid naval mines in the Strait of Hormuz, how long would it realistically take to reopen a major chokepoint for commercial shipping?

Scott Savitz: Iran depends on the Strait of Hormuz for its own commercial traffic, so it will likely prefer to mine other areas of the Gulf, as it did in the 1980s. It can selectively target ships in the Strait of Hormuz using other weapons, such as missiles and explosive-laden boats (with or without people aboard). The speed with which mined waters can be reopened depends on risk tolerance and resource commitment. Tankers were willing to run the gauntlet of mine risk in the Persian Gulf during the 1980s, paying correspondingly elevated insurance rates, and some of them were damaged. For commercial ships, it’s a cost-benefit calculation, based on the best available risk data from military sources. For military vessels, it depends on the urgency and impact of what they’re trying to achieve relative to the risks from mines, taking other risks into account. I’ve suggested that large commercial ships could be remotely controlled and filled with foam for expedited mine clearance, by having these large USVs repeatedly traverse a minefield.

Taiwan’s Naval Mining Potential

CRR: You’ve written extensively about defending Taiwan with naval mines. What is Taiwan’s current capacity to lay mines at scale? Do they have the inventory, the delivery platforms, and the trained personnel to execute rapid minelaying before a PLA amphibious force arrives? What about the ability to replenish mine fields? How might UUVs fit into this, both as a mine-laying platform, but also as a PRC offensive “first wave” vessel to clear mine fields?

Scott Savitz: I can’t speak to Taiwan’s current mining capabilities in an unclassified context. I can only say that they are increasingly recognizing the importance of mining as part of a “porcupine strategy” to help counter a Chinese invasion, and have acquired capabilities and capacity in recent years. Low-profile USVs and/or UUVs can be used to stealthily lay mines in otherwise inaccessible waters. The People’s Liberation Army Navy could also use large remotely controlled ships as USVs to try to clear minefields, along the lines of what I’ve described above.

Mine Longevity and the Persistence Problem

CRR: How long do mines actually last once they’re in the water? A personal obsession is advanced batteries’ military applications — would more capable, denser, longer-duration batteries prove useful for a Taiwan Strait defense that might need to persist for months? I know you’ve grappled before with some legal, ethical, and practical questions regarding naval mining and persistence.

Scott Savitz: Some World War I and World War II mines are still in waters from the Baltic to the Pacific, and those remain no-go areas because they haven’t been cleared, and the mines could still be active. Mines that use electronics inevitably can’t function once their batteries expire, but that can take months or longer. Battery life could be important in this context, and increasing the energy density of batteries or simply increasing their size can be advantageous.

Mines and Energy Coercion Against Taiwan

CRR: In a scenario short of a full invasion — say, a PRC quarantine or blockade aimed at depriving Taiwan of LNG, oil, and coal imports — how might mines figure in? Could the PRC mine Taiwan’s port approaches to choke off energy deliveries without triggering the kind of full-scale military response an amphibious invasion would? Conversely, could Taiwan or the U.S., if necessary, use offensive mining to threaten PRC maritime shipping, whether international or coastwise?

Scott Savitz: China could use submarines or ostensibly commercial ships to stealthily lay mines around Taiwanese ports; it could even lay them overtly from aircraft. Inevitably, Taiwan would conduct MCM operations to clear the minefields. If Chinese forces were targeting MCM forces to prevent the Taiwanese from doing so, and/or could reseed the minefields faster than Taiwan could clear them, the mines could pose a sustained threat. Again, though, some commercial ships might brave the minefields if the risk-to-reward ratio were right.

Conversely, the U.S. or Taiwan could potentially use naval mines to blockade Chinese ports, if they can stealthily lay and reseed the minefields more effectively than China can clear them.

Artificial Intelligence and Naval Mining

CRR: Could advances in AI transform naval mining, either from a defensive or offensive perspective?

Scott Savitz: Mines with AI could be more capable of distinguishing sweeps from target ships, or could be more selective about which ships to damage. On the MCM side, AI could help in interpreting large quantities of ISR data regarding adversary mining capabilities and efforts. It could also help with minehunting by accelerating the classification and identification of mines. However, given that AI systems can make errors that humans wouldn’t, it will take a lot of testing and well-earned trust for AI to be relied upon in mine warfare.

Joseph Webster is a senior fellow at the Atlantic Council’s Global Energy Center and the Indo-Pacific Security Initiative; he also edits the independent China-Russia Report. Tony Jing, a student at the University of Wisconsin-Madison, provided research assistance for the article, although any errors are Webster’s alone. This article’s questions reflect their own personal opinions.

The China-Russia Report is an independent, nonpartisan newsletter covering political, economic, and security affairs within and between China and Russia. All articles, comments, op-eds, etc represent only the personal opinion of the author(s) and do not necessarily represent the position(s) of The China-Russia Report.