# The Korea Strait
> Between the Korean Peninsula and Japan, this passage carries over 90% of Japan's energy imports and is a contested naval transit route for US, Chinese, and Russian forces.

**Meta:** type: reference · date: 2026-07-03 · heads:  · 4 takes · 4 lenses · 3 regions

## What it is

The Korea Strait is the sea passage linking the East China Sea and Yellow Sea to the Sea of Japan, running approximately 243 kilometres between the southern tip of the Korean Peninsula and the Japanese island chain of Kyushu and Tsushima. Tsushima Island bisects the passage into two channels: the Western Channel, narrower and deeper (reaching 227 metres), which runs between South Korea's Busan coast and Tsushima; and the broader Eastern Channel, also called the Tsushima Strait, between Tsushima and Kyushu. At its narrowest the waterway spans roughly 23 nautical miles, of which 17 qualify as international high seas freely transitable under UNCLOS. Three states hold shoreline or island interests: South Korea, Japan, and North Korea.

## History

Korean and Chinese merchants used the strait for centuries before it became, on May 27-28, 1905, the site of the Battle of Tsushima. Admiral Togo Heihachiro's fleet destroyed almost the entire Russian Baltic Fleet in those two days, ending the Russo-Japanese War and establishing Japanese naval dominance in Northeast Asia. Japan's resulting supremacy persisted through its 1910-1945 colonial occupation of Korea, during which it controlled both shores of the strait. After 1945, division of the peninsula placed the northern approach under split governance: South Korea on the western shore, North Korea controlling the northern coast. Japan and South Korea normalised relations in 1965, but a persistent dispute over the Dokdo/Takeshima islets, claimed by both states and administered by South Korea, introduces periodic diplomatic friction. Both countries maintain formal free passage for commercial shipping under international maritime law.

## Current state

The most systematic traffic survey, using Japanese government data compiled from Lloyd's information in 1996, recorded approximately 7,387 vessels completing 75,293 voyages annually through the strait. Regional trade growth since then has substantially increased throughput. Japan's energy exposure is acute: more than 90% of Japan's oil and gas imports transit the Korea Strait on their final leg from the Strait of Malacca and South China Sea to domestic ports. South Korea's container exports to North America also route through the strait before entering the Pacific.

China's People's Liberation Army Navy has expanded its use of the strait as an exit to the western Pacific. In August 2025, a Chinese-Russian joint naval patrol transited through the Sea of Japan following bilateral exercises; Japanese and South Korean patrol aircraft shadowed the passage. Between June 26-30, 2026, eight Chinese navy vessels transited Japan's stretch of the first island chain toward the Pacific, a continuation of a documented pattern. US 7th Fleet vessels transit the strait regularly in support of bases in both Japan and South Korea.

## Relationships

The Korea Strait connects the two US treaty allies most exposed to North Korean military action. The growing fortification of the [North Korean side of the DMZ](/ar/n/korea-dmz-seoul-eases-north-fortifies) makes any peninsula contingency a strait scenario: North Korea's Wonsan and Chongjin ports open onto the Sea of Japan through the same passage that carries Japan's energy supply. Japan and South Korea deepened defense ties at the June 2026 Koizumi-Seoul summit; the [resulting agreements](/ar/n/japan-korea-defense-koizumi-seoul-jun28) include shared maritime domain awareness and anti-submarine cooperation. China's expanding surface fleet and submarine force treat the strait as a primary Pacific exit, putting it at the intersection of US-China naval competition documented in the [global chokepoints backgrounder](/ar/n/shipping-chokepoints-chokepoints-backgrounder). North Korea's documented use of the Sea of Japan corridor for sanctions-busting ship-to-ship oil transfers, tracked in the [maritime evasion dossier](/ar/n/north-korea-maritime-oil-evasion-2026), adds a sanctions-enforcement dimension.

## What to watch

The Japan-South Korea defense agreements from June 2026 will be tested by political durability in Seoul, where public opinion on Japanese defense cooperation is volatile. China and Russia's pattern of joint naval transits will set the baseline for how freely the People's Liberation Army Navy treats the passage over the next decade. Japan's dependence on the strait for more than 90% of its oil and gas imports makes it a first-order energy security variable: any contingency on the [Korean Peninsula](/ar/n/korean-peninsula-dossier) would immediately affect Japanese energy costs and supply. North Korea's commissioning of the Choe Hyon destroyer in mid-2026, its first nuclear-capable surface combatant, introduces a new maritime threat vector in the same waters.

## Regional takes (batched by bias / lens)

### official record
- **IEA, Japan Energy Profile** (Japan, en) — IEA standing country profile documenting Japan's near-total dependence on seaborne energy imports, with oil and LNG accounting for roughly 90% of primary energy supply, the bulk of it transiting the Korea Strait on the final leg from the Strait of Malacca.
  Source: https://www.iea.org/countries/japan

### strategic analysis
- **Observer Research Foundation, Why the Tsushima Strait is vital for Northeast Asia's geopolitics** (India, en) — March 2023 analysis by Pratnashree Basu at ORF: documents Japan's dependence (more than 90% of oil and gas imports through the strait), the strait's function as the primary logistics entry point for US military forces in Japan and South Korea, and China's growing use of the passage for Pacific naval projection.
  Source: https://www.orfonline.org/research/why-the-tsushima-strait-is-vital-for-northeast-asias-geopolitics

### maritime policy research
- **Nautilus Institute for Security and Sustainability, A Vessel Traffic System Analysis for the Korea/Tsushima Strait** (United States, en) — 1997 analysis by Linda Paul using 1996 Japanese government data compiled from Lloyd's: 7,387 vessels completed 75,293 voyages that year; 1,069 tankers made 9,597 passages; vessels over 20 years old accounted for 26% of total voyages, raising oil-spill and accident risk concerns.
  Source: https://nautilus.org/esena/a-vessel-traffic-system-analysis-for-the-koreatsushima-strait/

### oceanographic survey
- **Oceanography (The Oceanography Society), Korea/Tsushima Strait** (United States, en) — Peer-reviewed oceanographic profile of the Korea/Tsushima Strait documenting the two-channel bathymetry (Western Channel max depth 227m, broader Eastern Channel), Tsushima Current transport, and seasonal variability in through-flow from the East China Sea to the Sea of Japan.
  Source: https://tos.org/oceanography/assets/docs/19-3_teague.pdf

## Across the graph
- Related: [[korea-dmz-seoul-eases-north-fortifies]], [[korean-peninsula-dossier]], [[shipping-chokepoints-chokepoints-backgrounder]], [[north-korea-maritime-oil-evasion-2026]], [[japan-korea-defense-koizumi-seoul-jun28]]
- Entities: Place:korea Strait, South Korea, Japan, North Korea, China, Russia

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Canonical: https://rbtfl.xyz/ar/n/korea-strait-dossier