The dangers facing oil tankers carrying their vital cargo over long distances haunt leaders worldwide and animate their discussions about naval procurement. Military analysts in countries such as China and India have begun to assert that their countries need their own blue-water navies to protect tankers on their journeys from foreign terminals to home ports.

This argument is understandable given that much of the world's oil supply travels by sea. The United States, the world's largest oil consumer, imports 60 percent of the oil it consumes, over 95 percent of which arrives by sea. Japan, the world's third-largest oil consumer, is almost completely dependent on maritime imports. In 2005, China imported 46 percent of the oil it consumed, India 68 percent. By 2025, import figures are expected to balloon to 75 percent of total consumption for China and approximately 85 percent for India. Both bring in roughly 90 percent of their imported oil by sea.

Most of these countries rely on the safe transport of oil through one 21-mile-wide waterway: the Strait of Hormuz, which leads out of the Persian Gulf into the Indian Ocean and through which 16.5-17.0 million barrels of oil were shipped daily in 2004 (accounting for nearly 25 percent of global oil shipments). Oil bound for China, Japan, and the West Coast of the United States from the Middle East must also transit the Strait of Malacca and the Strait of Singapore, both of which carried 11.7 million barrels per day in 2004. These passageways are the chokepoints where the potential for the disruption of tanker traffic by terrorist attacks or naval blockades is greatest.

But in reality the risks to maritime flows of oil are far smaller than is commonly assumed. First, tankers are much less vulnerable than conventional wisdom holds. Second, limited regional conflicts would be unlikely to seriously upset traffic, and terrorist attacks against shipping would have even less of an economic effect. Third, only a naval power of the United States' strength could seriously disrupt oil shipments, but the United States is more likely to protect shipping on the high seas than to do anything to endanger it. Fourth, if any country attempted to interfere with international shipping, a coalition would inevitably form to keep traffic flowing with manageable damage to oil deliveries and the global economy. finally, although all-out wars between major powers can seriously disrupt maritime shipping, the chances of such a conflict happening in the foreseeable future are remote.


Twentieth-century history underscores the difficulty of significantly disrupting commerce at sea. Attacking commercial ships has been an effective means of achieving political objectives only when employed by major powers in wars of national survival. U.S. operations in the Pacific in World War II imposed serious hardships on Japan; the British blockade of Germany during World War I and German operations against Allied shipping in the Atlantic during both world wars were also quite successful. Blockades have been used selectively for more limited purposes but only under unique geopolitical circumstances. In 1962, for example, a U.S. blockade helped defuse the Cuban missile crisis, and Iraqi oil was successfully embargoed by a maritime coalition in support of UN sanctions after 1991.

Lesser naval powers have lacked the capability to blockade major shipping routes, even when fighting all-out wars. The most notable example comes from the Iran-Iraq War, during which the opposing sides attacked shipping in the Persian Gulf to weaken each other in their stalemated conflict. Iran, in particular, had an advantageous geographic position to selectively interdict tanker traffic passing through the Persian Gulf. But neither it nor Iraq achieved much success, despite 544 attacks that killed over 400 civilian sailors and injured another 400. Although commercial shipping in the Gulf initially dropped by about 25 percent and the price of crude oil spiked, the so-called tanker war did not in the end significantly disrupt oil shipments. In fact, the price of crude soon started to fall steadily, partly because Iran lowered its prices to offset higher insurance premiums on shipments. In 1987, the United States offered to protect Kuwaiti ships by outfitting them with U.S. flags and escorting them, which deterred further attacks. Even at its most intense, the tanker war failed to ensnare more than two percent of the ships traveling through the Persian Gulf.

Recent trends concerning oil tankers make it even more difficult to disrupt maritime oil shipments. The size and the strength of the global tanker fleet have increased markedly over the last two decades. From 1980 to 2006, the number of tankers grew from 2,516 to more than 10,400, and the average capacity of each tanker increased by 400 percent, with a disproportionate amount of the new tonnage having been added in recent years. Single-hulled tankers are being phased out in favor of more resilient double-hulled ones.

The greater number of tankers traveling at higher speeds and in more congested shipping lanes makes it increasingly difficult to identify and intercept them. This is especially true for submarines, which have a limited ability to identify surface ships and have only a small onboard supply of torpedoes and antiship missiles. If a submarine attacks a ship using just two torpedoes, it will have exhausted more than a tenth of its standard arsenal. Meanwhile, other potential targets nearby will disperse, forcing the submarine to relocate. A single conventional-power submarine (Iran has only three) facing no opposition could realistically expect to damage about half a dozen oil tankers in a busy sea-lane several hundred miles wide over the course of a month, disrupting at most a tiny fraction of the oil deliveries made during that period. Conventional-power submarines, moreover, are relatively slow and cannot catch modern tankers, which travel at 15-20 knots.

Mines and conventional-warhead missiles are even less effective now against large modern tankers than they were in the past. During the Iran-Iraq War, several oil tankers ran over mines in the Strait of Hormuz, but they sustained little damage due to their size and the protective effect of the liquid petroleum they carried (petroleum is not explosive in the airless tanks, and its weight holds the hulls in place). Even the most modern antiship missiles have relatively small warheads that are designed to damage the sensors and weapons systems of surface warships but are not capable of sinking or disabling a large tanker. Most missiles shot at a tanker would explode on its large deck, causing minimal damage. Even if they penetrated the deck, they would explode inside tanks where the liquid oil or the water in ballast would absorb the blast without igniting. In order to disable a modern-day tanker, an attack would have to include a salvo of eight to ten missiles with conventional warheads; a sustained campaign would quickly exhaust the missile stockpile of a medium-sized military power.


There are only a few locations where the potential risks to international tanker traffic are great: the Strait of Hormuz, at the mouth of the Persian Gulf, and the Strait of Malacca and the Strait of Singapore, in Southeast Asia. Fortunately -- and contrary to popular perception -- these waterways are in little danger of being blocked.

Iran has the capacity to attack the Strait of Hormuz from its shore, using coastal antiship missiles (such as Chinese Silkworm missiles), patrol boats, and short-range aircraft flying from nearby bases. It could also employ small, high-speed boats packed with high explosives to ram oil tankers and hostile naval vessels. But if it ever decided to target ships transporting oil from the Persian Gulf, it would have to interfere with the shipping of many neutral nations. As during the tanker war of the 1980s, a coalition of nations that have an interest in the free flow of oil from the Persian Gulf would quickly form. The United States, with the support of other nations with capable navies and the Persian Gulf states, could neutralize Iran's attacking forces with a combination of actions at sea and attacks against command-and-control facilities, missile sites, ports, and airfields along the Iranian side of the strait. The virtually certain result would be a swift defeat of the Iranian interdiction effort.

The disturbance would take an economic toll but hardly an unmanageable one. Special premiums would have to be paid to the crews of tankers passing through the strait during the early stages of such a campaign, and insurance rates would be higher, but governments could collectively indemnify shippers. The number of ships ultimately stopped by Iran's actions would amount to a single-digit percentage of all the traffic passing through the Strait of Hormuz, and even this disruption would prove short-lived.

Likewise, little damage to international shipping is likely in Southeast Asia. The countries that could most effectively interfere with traffic in the Strait of Malacca and the Strait of Singapore are the three littoral nations, Indonesia, Malaysia, and Singapore. Currently, far from threatening to interfere with shipping, these countries cooperate to protect it, and it is difficult to conceive of a reason they would change their behavior.

Furthermore, disrupting shipping in this waterway is a tall order. At its western end, close to the Andaman Sea, the Strait of Malacca is 230 miles wide. It is narrowest to the east -- three miles -- where it takes a north-south direction and becomes the Strait of Singapore. Pirate attacks regularly occur at both ends, but these are generally hit-and-run robberies. Terrorist groups could achieve little more. Although a terrorist group or the navy of a state other than Indonesia, Malaysia, or Singapore could covertly deploy a small number of mines in this shipping channel, a single mine cannot sink a large tanker, and once detected, covertly laid mines could be cleared by Singapore with outside assistance. Singapore has a very effective local navy and would enjoy strong support from other countries in countering such harassment. Even if terrorists scuttled an oil tanker in the Strait of Singapore, it would not block the waterway any more than a single broken-down car would halt all traffic on a 20-lane highway. And in the worst-case scenario -- if shipping through the strait were crippled -- ships could temporarily resort to alternate, if longer, routes around Lombok, of the Lesser Sunda Islands, or even south of Australia.


Only a navy that can dominate a large area of water over a long period of time can seriously disrupt tanker traffic. Effectively detecting, identifying, intercepting, and, if necessary, dispatching boarding parties onto or forcibly stopping ships passing through a blockade area requires a large number of surface ships equipped with embarked helicopters and supported by maritime patrol aircraft. Today, the U.S. Navy has no rivals in its capacity to impose and sustain such blockades. China, India, Japan, and Russia are the only other countries with the economic potential to build large blue-water navies in the same league with the United States', but they are still at least 20 years away from developing the fleet strength, naval-supply networks, and operational skills needed to mount sustained blockades far from their home ports.

The United States has employed and will likely in the future continue to use naval blockades when necessary. For example, in the event of a conflict between China and Taiwan that draws in the United States, the United States might legally declare a war zone along the coast of southern China and intercept shipping several hundred miles at sea, causing major interruptions in the flow of oil and vital materials that the Chinese navy could do little to stop. If Chinese warships, submarines, and aircraft came out to challenge the blockade, superior U.S. naval and air forces would overcome them. Similarly, in the event of a crisis involving North Korea, the United States, South Korea, and Japan could together keep almost all shipping from entering or leaving North Korean ports.

Granted, these campaigns would have serious repercussions. Blockading China's shipping in a conflict over Taiwan would risk escalation. And Pyongyang has declared that even a UN-endorsed blockade would be an act of war. Nevertheless, the military reality is that the United States is unique in the world today in its ability to sustain effective naval blockades.

This U.S. naval hegemony, however, need not be unsettling to other countries. The United States has a very long tradition of promoting and protecting the free flow of trade over the world's seas. When Washington has used its naval dominance to blockade shipping, it has done so judiciously. During the Cuban missile crisis, for example, a naval blockade was employed instead of direct military attacks. In the Vietnam War, a blockade was imposed only many years into the war, and the shipping of neutral nations was allowed to pass safely through. The embargo of Iraqi oil shipments in the 1990s was a multilateral campaign supporting UN resolutions. Nothing in the United States' foreign policy tradition indicates that the country would abuse its maritime power for its own narrow interests.

Washington, nevertheless, understandably bears the burden to reassure other countries in this regard through its diplomacy and military-to-military programs. It must persuade them that the world benefits from U.S. naval supremacy and that they need not fear U.S. interference of maritime commerce so long as they do not endanger Washington's vital interests. Indeed, with the single exception of a potential conflict over Taiwan, the major maritime powers of the future -- China, India, Japan, and Russia -- should find themselves cooperating with the United States to protect international shipping or using multilateral blockades to enforce international norms of conduct against outlaw states or nonstate groups.

A close examination of the naval capabilities of China, India, Japan, and Russia casts doubt on their capacity to seriously interfere with one another's oil shipping in the short to medium term, let alone global oil supply lines. These four countries could feasibly impose discriminating blockades, including blockades of oil deliveries, on vulnerable nations with smaller navies, but such action would require international support, or at least a lack of international opposition.


When a country cannot deploy the full range of naval forces necessary for a targeted blockade, it can try to interfere with any and all shipping by deploying mines, submarines, or aircraft. In conducting such an indiscriminate campaign against an adversary, however, the aggressor must consider the reaction of third parties whose shipping interests will inevitably be affected. Historically, neutral countries and countries concerned with free maritime traffic have tended to band together and reflag ships, provide escorts, and place great pressure on the disruptive countries.

The navies of China, India, Japan, and Russia already have the capability to conduct serious campaigns of harassment against shipping generally or to impose targeted blockades on vulnerable nations with smaller navies. But the farther away these operations were from their home ports, the less effective the actions would be and the more likely that they would be stopped by concerted international action. For example, although India has significant capabilities to patrol the coast of Pakistan and selectively stop oil shipping there, it would find conducting a similar operation in oil shipping lanes farther afield more difficult. Such actions against international shipping would also provoke immediate opposition from the international community -- especially the United States. A multinational maritime force would have little difficulty suppressing the threat and keeping sea-lanes open.

Consider a Chinese blockade of Taiwan. Chinese aircraft flying from coastal bases could track and identify ships approaching Taiwan, and Chinese warships could easily stop, inspect, and divert specific vessels. Taiwan's naval and air forces would put up a good fight in contesting the blockade, but they would be worn down in a matter of weeks by the larger Chinese force. The blockade would cause severe economic hardship in Taiwan. But if the United States and the international community considered the blockade unjustified, international pressure for a settlement would be intense, and the blockade could be lifted by an opposing maritime coalition led by the United States.

Even mines, which can be dropped covertly from fishing vessels and other merchant ships, would have a limited effect on traffic. The combined surveillance, intelligence, and antimine capabilities of the major maritime nations would be able to identify the country laying the mines; find, isolate, and clear the minefields; and restore shipping in a matter of weeks.


The resilience of today's tanker fleet and the realities of naval power mean that effecting a serious and sustained disruption of international oil shipping is a much more difficult task than is generally imagined. Even the critical chokepoints of maritime commerce could be kept open in the face of attempts by countries or terrorists to wreak havoc in them.

Over the next two decades, no country other than the United States will have the ability to pull off any consequential disruption of traffic. The real challenge is thus a matter of diplomacy: Washington should, through its words and its conduct, maximize the chances that others will join it in coalitions of the willing when necessary and assure other countries that its supremacy will continue to be used to guarantee the freedom of the seas.

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  • Dennis Blair is former Commander in Chief of U.S.
    Pacific Command. Kenneth Lieberthal is Professor of Political Science at the University
    of Michigan and served as Senior Director for Asia on the National Security Council
    from 1998 to 2000.
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