Going back to 1597 to understand why the ocean current is an intimate friend of the Korean diver

It is widely accepted that maritime power is also a visible manifestation of the power of the state, with every great power today aspiring to maintain a great navy as a symbol of its status. In essence, maritime power is about transportation. The unique characteristics of water offer transportation possibilities that are markedly different from those found on land or in the air. This mindset is not new. The great empires of the 17th to 20th centuries cannot be adequately understood without a consideration of the naval and mercantile power that they were able to wield.

Lesser-known history, which remains a significant tale for most Koreans and Japanese, tells of the great Battle of Myeongnyang, fought on October 26, 1597. Here, the intimate knowledge of ocean currents became the deciding factor in the victory of one profound power against another.

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The Battle of Myeongnyang, where 133 Japanese warships outnumbered 13 Korean warships © Hyeonchungsa (Admiral Yi’s Shrine) Shrine Office of Cultural Heritage Administration, Republic of Korea

South Korea is mostly surrounded by water and has 2,413 kilometres of coastline along three seas. To the west is the Yellow Sea; to the south is the East China Sea. The country is bordered by China to the northwest and Russia to the northeast. It is separated from Japan to the east by the Korea Strait and the East Sea.

The sea currents circulate in a counterclockwise direction. The Kuroshio (Japan Current), the Tsushima Current and the East Korea Warm Current bring warmer and more saline water to the north. There they merge into the Tsugaru Current and flow into the Pacific Ocean through the Tsugaru StrKoait. They also feed the Sōya Current and exit through the La Pérouse Strait to the Sea of Okhotsk. The returning branch is composed of the Liman, North Korea and Central (or Mid) Japan Sea currents, which bring fresh and cold water along the Asian coast to the south.

The sea has complex tides, which are induced by the tidal waves of the Pacific Ocean penetrating through the Korea Strait and Tsugaru Strait. Mixed tides occur in Peter the Great Gulf and the Korea Strait. The tidal waves have a speed of 10–25 cm/s in the open sea. They accelerate in the Korea Strait (40–60 cm/s), La Pérouse Strait (50–100 cm/s) and especially in the Tsugaru Strait (100–200 cm/s).

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Korean divers securing their location at Young Jin with jonlines against strong currents © Hyun Duk Kim

Apart from tides, the water level also experiences seasonal, monsoon-related variations across the entire sea, with the highest levels observed in summer and the lowest in winter. Wind may also locally change the water level by 20 to 25 cm; for example, in summer it is higher at the Korean coast and lower at the Japanese coast.

Without doubt, one historical figure knew more than most about these dramatic changes and flows: Admiral Yi Sun-sin. His maritime strategy was so impressive, naval schools today continue to teach it. During the Japanese invasions of Korea (1592–1598), Yi defeated the Japanese 23 times. What was even more intriguing is Korea, called Joseon at the time, did not have any naval training facilities.

Admiral Yi studied numerous sites for his last stand against the Japanese navy and decided on luring them into the Myeongnyang Strait. It was obvious that the Japanese would enter the strait when the tide was favourable, so he didn’t want to fight south of the strait, with the current at the attacker’s advantage. Instead, he fought in the waters just north of the strait, where the currents were calmer. The strait had very strong currents that flowed at approximately 10 knots, first in one direction, then in the opposite direction, at three-hour intervals.

Admiral Yi Sun-sin was famed for his victories against the Japanese navy during the Imjin war in the Joseon Dynasty, and was well-respected on and off the battlefield, even by Japanese Admirals © Hyeonchungsa (Admiral Yi’s Shrine) Shrine Office of Cultural Heritage Administration, Republic of Korea

Admiral Yi realised he could use this unique condition as a force multiplier. The narrowness of the strait would prevent the Joseon fleet from being flanked by the numerically superior enemy fleet, and the roughness of the currents prevented the Japanese from effectively manoeuvring, forcing them to attack in smaller groups and making it difficult to get close to the Korean ships. Furthermore, once the tide changed, the flow of the current would in effect push the Japanese away from Yi’s fleet and the momentum could be harnessed to increase the effectiveness of a counterattack.

Yi described about “200 enemy ships … flowing [into the strait]” and at least 133 ships in his immediate vicinity. It is estimated that at least 133 ships were warships and at least 200 ships immediately behind were logistical (supply and troop-carrying) support ships.

The tide soon shifted and the Japanese ships began to drift backwards and collide with each other. In the confusion, Admiral Yi ordered his ships to advance and press the attack, plunging into 30 Japanese ships. The dense formation of Japanese ships crowded in the narrow strait made a perfect target for Joseon cannon fire.

The immediate results of the battle were a shock to the Japanese command. While the rest, as they say, is history, the main takeaway seemed to be one man’s huge advantage based on ocean wisdom.

Popular sites are frequented by local divers, here taken in Sok-cho © © Hyun Duk Kim

Today, while most non-divers are afraid of the current when they play at the shore, it is a fun tool for the “hydro sapien”. It is said that the Korean diver is used to dealing with strong currents and can handle strong tidal changes well. In fact, most open-water divers will fight currents just to move during a basic course.

The dramatic differences in water temperature and tidal flow in the north and south creates great diversity in Korean waters, all still relatively unexplored by those outside the country. It may be the next frontier of some of Asia’s best diving yet.

This article was published in Asian Diver “Go With The Flow” Issue 3/2015

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