Last week, Donald Trump announced a new class of U.S. Navy battleships, which will be named after him. The Navy said that the new warship type “will be the most lethal surface combatant ever constructed.” The president portrayed the move as a boost for American shipbuilding and vowed to be personally involved in the ships’ development. “The U.S. Navy will lead the design of these ships along with me,” he said, “because I’m a really aesthetic person.” Yet the “Trump class” battleship program seems optimized more to produce a scary-looking vessel than to address the rapidly changing threats to American military power on the open seas.

Late last month, Ukraine’s military signaled a major shift in how wars between nations will be waged in the coming years. Using the country’s homegrown Sea Baby naval drones, Ukrainian forces badly damaged two oil tankers off the coast of Turkey, in the Black Sea. Shortly thereafter, another oil tanker was attacked, reportedly also by the Ukrainians, in waters thousands of miles away, in the Atlantic Ocean, off the coast of Senegal. A similar attack on a tanker occurred earlier this month in the Mediterranean Sea.

All of these vessels are believed to be part of the so-called shadow fleet of tankers that, despite multinational sanctions against Russia, have been sailing the world’s oceans and delivering large quantities of Russian oil. Disrupting the invader’s oil industry, thereby starving the Kremlin of revenue, has become essential to Ukraine’s survival, and the use of cheap weaponry to disable faraway oil tankers is a crucial part of the country’s military strategy.

The conflict that began with Russia’s full-scale invasion of Ukraine in 2022 has revealed the erosion of many post–World War II norms, including on the high seas. After many decades of relative peace on the world’s oceans, one can easily forget that civilian ships were once a routine target of military operations during wartime. But long-range anti-ship technology has become so effective—and so cheap relative to other ways of attacking an enemy—that the risk to merchant vessels will rise sharply. Even countries such as Ukraine, which has limited means and minimal naval experience, can thwart their enemies’ maritime interests in ways that have been almost unthinkable for 80 years.

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Deliberate attacks on civilian shipping were widespread in the first half of the 20th century. Both world wars included major campaigns to destroy commercial shipping, resulting in the sinking of many millions of tons of merchant vessels. During both conflicts, German U-boats attacked vessels in waters all around the world, with the goal of starving the United Kingdom of supplies and forcing it to sue for peace.

Over time, naval practices adapted to the submarine threat. By using convoys—large groups of merchant vessels protected by British, American, and Canadian escort vessels—the Allies were able to better protect their shipping. An intense technology race occurred between submarines and their pursuers. The development of sonar, radar, long-range aircraft, and self-guided weapons helped tilt the balance against the U-boats. Ultimately, the Allies destroyed so many enemy submarines that the campaign became too expensive for the Germans to continue.

Since then, Germany’s defeat in both world wars has served as a cautionary tale to countries that might be inclined to target civilian shipping, and the overwhelming dominance of the U.S. Navy has further dissuaded most other nations’ armed forces from attempting similar campaigns. Yet however much the threat to civilian ships has disappeared from the public mind, a successful war against merchant trade could be devastating. By one estimate, approximately 90 percent of world trade is carried by ships. The scale of this movement of goods and raw materials—without which much economic activity around the world would simply cease—requires a global fleet of about 50,000 merchant vessels with crews totaling more than 1 million merchant sailors, according to the International Chamber of Shipping.

In this context, what the Ukrainians have been doing since November is ominous. In the next large state-to-state war, Russia’s shadow oil tankers won’t be the only casualty, and naval drones such as the Sea Baby won’t be the only culprits. Submarines, so consequential during World War II, remain potent weapons for sinking merchant ships—particularly in combination with other technologies. Anti-ship missiles, launchable from the air or the ground, are more accurate and destructive than ever, and have gained longer range. Aerial drones, which have become ubiquitous in the war in Ukraine, both on the battlefield and in the attacks on city and civilian infrastructure, represent a further threat.

Merchant ships, using their own resources, cannot reliably defend themselves against these technologies. Even if they travel in convoys protected by warships and aircraft, efforts to fend off all drone and missile attacks could easily fail because of the cost differential between offensive and defensive weapons. Systems to attack shipping are inexpensive, and equipping even large warships with sufficient weaponry to protect them will be an enormous challenge.

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The Ukrainians have used unmanned aerial vehicles to attack Russian naval bases and logistics infrastructure, and their anti-ship missile, the Neptune, sank the largest Russian warships in the Black Sea. Even though none of these systems is as powerful as their Western or Chinese equivalents would be, they have done extraordinary damage to Russian naval capabilities.

A war between large powers, such as the United States and China, would be devastating for worldwide shipping. But the fundamental difficulty of defending shipping extends to warships as well. U.S. aircraft-carrier battle groups may be the world’s most expensive concentrations of weapons systems. They are made up of a range of warships, including the carriers themselves—the newest of which, the USS Gerald R. Ford, cost an estimated $13 billion. They carry large numbers of F-35s, some of the most expensive aircraft in the world. And they are also crewed by thousands of specialized sailors, who cannot be replaced quickly. And yet, for all their extraordinary cost and value, carriers are vulnerable to attack and must be defended primarily by escorting vessels.

The Chinese would only have to calculate the number of missiles and drones the U.S. could intercept at any one time and deploy more than that—which, considering Chinese manufacturing capacity, would not be a challenge. The balance of power in naval warfare is shifting from the ships that seek to defeat outside attacks to the technologies that do the attacking.

The implications in the Pacific Ocean are frightening for the U.S. Navy—and offer one more reason, based on present trends, the United States is poised to lose an extended war in the region. A strategy that failed the Germans in the world wars is far more likely to succeed today, and the impact on the global economy and power balance could be profound.