Wikipedia Deep Dive

First island chain

12 min read

The Fence Around a Rising Power

Imagine drawing a line on a map. Start at the frozen tip of Russia's Kamchatka Peninsula, sweep down through Japan, hook past Taiwan, and keep going until you reach the tropical shores of Borneo. That arc of islands—thousands of miles long—isn't just geography. It's one of the most strategically contested stretches of real estate on Earth.

American military planners call it the first island chain.

To understand why this matters, you need to think like a naval strategist. If you're China, looking out from your coast at the Pacific Ocean, you don't see open water. You see a wall. A string of islands, most of them either American allies or American territory, stretching like a picket fence from north to south. And behind that fence? Every major American military advantage in Asia.

What Exactly Are We Talking About?

The first island chain isn't a formal geographic term you'd find in a geology textbook. It's a strategic concept, a way of organizing how military planners think about the western Pacific. The chain includes the Kuril Islands (disputed between Russia and Japan), the entire Japanese archipelago, the Ryukyu Islands (which include Okinawa, home to massive American military bases), Taiwan, the northern Philippines, and Borneo.

These aren't random islands. They form a natural barrier, and the waters on either side behave very differently from a military perspective.

West of the chain—closer to mainland China—the seas are relatively shallow. The Yellow Sea and the East China Sea don't offer much depth for submarines to hide in. Shallow water is a submarine's nightmare. Sound travels farther. Detection becomes easier. A submarine trying to operate covertly in shallow water is like a spy trying to blend in at a small dinner party rather than a crowded street.

East of the chain, the Pacific drops off into profound depths. Deep water means submarines can disappear. They can dive below thermal layers that scatter sonar, hide in underwater canyons, and operate with far greater freedom.

Why China Sees a Cage

From Beijing's perspective, the first island chain looks less like geography and more like a deliberate American strategy to contain Chinese power. Chinese military planners use language that reveals their frustration—they describe it as a cordon sanitaire, borrowing a French term that means a buffer zone designed to isolate a threat.

This isn't paranoia. The United States does maintain substantial military forces throughout the island chain. American bases in Japan, including the sprawling complex on Okinawa, have hosted troops since World War Two. The Philippines, despite occasionally rocky relations with Washington, still hosts American forces under a visiting forces agreement that dates back over seventy years. In 2023, the Philippines announced four new bases would be available to American troops.

For China's navy, particularly its submarine force, this geography creates a fundamental problem.

Modern naval strategy puts enormous value on ballistic missile submarines—the boats that carry nuclear missiles and serve as the ultimate insurance policy against a first strike. The logic goes like this: even if an enemy destroyed all your land-based nuclear weapons, your submarines lurking somewhere in the ocean depths could still retaliate. This is called second strike capability, and it's what keeps nuclear deterrence stable.

But second strike capability only works if your submarines can actually hide. If China's ballistic missile submarines are stuck in shallow coastal waters where they can be tracked, they lose much of their deterrent value. The first island chain, in Chinese strategic thinking, is the barrier that keeps their submarines penned in.

Taiwan: The Keystone

Look at a map and Taiwan's importance becomes obvious. The island sits almost exactly at the midpoint of the first island chain, dividing the western Pacific into distinct northern and southern theaters.

General Douglas MacArthur, the famous American commander from World War Two and Korea, understood this immediately. He called Taiwan an "unsinkable aircraft carrier"—a permanent, immovable platform from which American and allied forces could project power across the entire region.

But the metaphor works in both directions.

If Taiwan were under Chinese control, that unsinkable aircraft carrier would be pointing the other way. More importantly, Taiwan's eastern coast drops steeply into deep water. Submarines operating from there would have immediate access to the Pacific depths where they could disappear from American tracking. Control of Taiwan would effectively punch a hole through the first island chain.

This is why Taiwan generates such intense strategic anxiety in both Washington and Beijing. It's not just about ideology or historical grievances. It's about the fundamental geometry of Pacific power.

The Shallow Waters Problem

To appreciate why water depth matters so much, consider how submarine detection works. The primary tool is sonar—essentially using sound waves to find objects underwater. In shallow water, sound waves bounce off the seafloor and surface, creating echoes and noise that actually makes detection easier in many ways. Submarines have fewer places to hide.

The South China Sea, which sits within the first island chain, offers China's navy more operational space than the Yellow Sea or East China Sea precisely because it's deeper. This explains, in part, why Beijing has been so aggressive about asserting control there—building artificial islands, claiming vast stretches of water within the controversial nine-dash line, and challenging other nations' vessels.

It's not just about fishing rights or national pride. It's about creating a protected space where Chinese submarines can operate without American interference.

How America Plans to Use the Chain

American strategists haven't missed any of this. Around 2009, a Japanese military strategist named Toshi Yoshihara and an American professor at the Naval War College named James Holmes began developing ideas for how the United States could use the first island chain's geography against Chinese naval expansion.

The concept is sometimes called archipelagic defense. Rather than trying to project power deep into Chinese waters—where American ships would be vulnerable to shore-based missiles and aircraft—the United States would use the island chain itself as a defensive barrier. American and allied forces positioned on the islands could use missiles, mines, and submarines to make passage through the chain extremely costly for any Chinese fleet.

Think of it like a medieval castle's approach. Instead of meeting the enemy in open battle, you force them to attack your fortified positions. The islands become the walls.

In 2014, the United States Naval Institute assessed that the first island chain represented the most effective point to counter any Chinese naval offensive. The logic was straightforward: rather than fighting across the vast Pacific, concentrate defensive power at the chokepoints the Chinese navy would have to pass through.

A 2019 article in the same publication went further, arguing that in the event of war with China, the American navy should establish a full blockade along the first island chain. This would effectively bottle up the Chinese navy in coastal waters, preventing it from reaching the open Pacific where it could threaten American territory or disrupt global shipping.

Japan's Transformation

For decades after World War Two, Japan maintained a strictly defensive military posture. The country's constitution, written under American occupation, renounced war as a sovereign right. Japan's military, called the Self-Defense Forces, existed primarily to protect the home islands and, crucially, to defend the American bases on Japanese soil.

This arrangement worked well during the Cold War, when the primary threat was the Soviet Union. Japan occupied a critical position blocking Soviet submarines from accessing the Pacific through straits between its islands. Japanese anti-submarine capabilities became world-class precisely because this mission was so important.

But China's rise has forced Japan to think differently about its role in the first island chain.

Starting in the late 2010s, Japan began deploying military assets to islands it had previously left largely undefended. Yonaguni, Japan's westernmost inhabited island, sits just 67 miles from Taiwan. Until recently, it had no military presence. Now it hosts radar stations and ground troops.

Japanese defense white papers—official government documents outlining security policy—increasingly emphasize threats from Chinese military expansion. The Japan Self-Defense Forces are developing capabilities specifically designed for island defense, including anti-ship missiles that could strike vessels attempting to pass through nearby waters.

The Marines Go Island-Hopping Again

For most of the past twenty years, American military planning focused on counterinsurgency—fighting irregular wars in places like Iraq and Afghanistan. But as those conflicts wound down, the Pentagon began pivoting toward what it calls great power competition, meaning potential conflict with China or Russia.

For the United States Marine Corps, this pivot meant returning to its World War Two roots: island warfare in the Pacific.

In 2020, the Marine Corps began fundamentally restructuring itself for operations along the first island chain. The concept involves small, mobile units equipped with anti-ship missiles and other weapons that can be rapidly deployed to islands throughout the chain. Rather than large, concentrated forces that make tempting targets, these distributed units would be harder to find and destroy while still posing serious threats to any enemy ships or aircraft in the area.

By 2021, the Marines announced plans for three additional Pacific-based regiments specifically designed for this mission. The 2025 National Security Strategy made the first island chain's defense an explicit American priority, noting the need "to deter adversaries and protect the First Island Chain."

Anti-Access and Area Denial

While the United States develops strategies for using the first island chain defensively, China has developed strategies for breaking through it offensively. Military planners call this Anti-Access/Area Denial, usually shortened to A2/AD—a concept worth understanding because it shapes so much of contemporary Pacific security thinking.

Anti-access capabilities are designed to prevent enemy forces from entering a region in the first place. Think of long-range missiles that could strike aircraft carriers or bases hundreds of miles away. Area denial capabilities make it dangerous for enemy forces to operate within a region even if they manage to get there—things like submarines, sea mines, and shorter-range missiles.

According to a 2018 Pentagon report to Congress, China's Anti-Access/Area Denial capabilities aimed at the first island chain are formidable—described as its "most robust." This means breaking through the chain, while theoretically possible, would be extremely costly. Conversely, the same report noted that China's ability to conduct military operations beyond the first island chain was "modest but growing."

This creates a strange equilibrium. China can probably prevent American forces from operating freely close to its coast. But China probably cannot project power effectively past the first island chain. Both sides are, in some sense, stuck.

The Philippines' Delicate Balance

Not every country in the first island chain shares America's enthusiasm for confronting China. The Philippines, in particular, has tried to balance its security relationship with Washington against its economic ties with Beijing.

The visiting forces agreement that allows American troops to train and temporarily deploy in the Philippines has been a recurring source of political controversy. In 2020, Philippine President Rodrigo Duterte announced he would terminate the agreement, only to reverse himself as tensions with China in the South China Sea escalated.

When Lloyd Austin, the American Secretary of Defense, thanked his Philippine counterpart Delfin Lorenzana in 2021 for retaining the agreement, it wasn't mere diplomatic courtesy. The Philippines occupies a critical position in the southern portion of the first island chain. Without Philippine cooperation, American strategy for the region becomes significantly more difficult.

The announcement of four new bases in 2023 represented a substantial expansion of American access—but the deal required careful negotiation and continued Philippine concerns about being caught in the middle of a superpower rivalry.

What Happens If the Chain Breaks?

Strategic concepts like the first island chain can seem abstract until you consider the consequences of their failure.

If China achieved control of Taiwan and secured passage through the island chain, the balance of power in the Pacific would fundamentally shift. Chinese submarines operating in the deep Pacific would pose threats to targets as distant as Guam or even Hawaii. Chinese surface ships could operate beyond the protective umbrella of shore-based missiles and aircraft, projecting power across the world's largest ocean.

Conversely, if the United States and its allies maintained an effective blockade of the first island chain during a conflict, China's navy would be largely confined to coastal waters. Its economy, dependent on seaborne trade for oil, food, and raw materials, would face devastating disruption. The manufacturing supply chains that make China the world's factory would begin to starve.

Neither scenario is inevitable. The first island chain isn't a static barrier but a dynamic space where both sides invest enormous resources trying to gain advantage. China builds more ships and missiles. America repositions forces and strengthens alliances. Japan rearms. The Philippines hedges. Taiwan fortifies.

The islands themselves don't move. But everything around them is in constant motion.

MacArthur's Ghost

It's worth returning to Douglas MacArthur for a moment, because his experience illustrates how quickly the strategic geography of the Pacific can shift.

Before World War Two, America's Pacific defense line ran from Hawaii through Guam to the Philippines—far out into the ocean, far from the Asian mainland. The Japanese attack on Pearl Harbor shattered that line in a single morning, eventually drawing the United States into the bloodiest conflict in human history.

Victory allowed America to push its defensive perimeter west to the Asian coast itself—the first island chain as we understand it today. What was once distant has become proximate. What was once American has become contested.

MacArthur understood that geography doesn't change, but control of geography does. The islands that seemed to guarantee American dominance in 1945 now require constant investment and diplomatic maintenance to remain in friendly hands. Taiwan, which MacArthur praised as an unsinkable aircraft carrier, could become the most dangerous flashpoint of the 21st century.

The Pacific is an ocean of distances that seem impossible to comprehend—yet those distances are spanned by missiles that fly faster than sound, submarines that cruise silently for months, and aircraft that can strike targets thousands of miles away. The first island chain matters because it's where all those capabilities, American and Chinese alike, come into closest contact.

That string of islands, from frozen Kamchatka to tropical Borneo, is where the peace of the Pacific will be maintained—or where it will unravel.