>>2894744 pb

http://www.antiquealive.com/Blogs/Mudflat_Korea.html

High tide and low tide differences perhaps.

Incheon infiltration

Incheon, South Korea, in pink coloring.

Fourteen days before the landing at Incheon, a reconnaissance team was placed in Incheon Harbor to obtain information on the conditions there. The team, led by US Navy Lieutenant Eugene F. Clark,[51] landed at Yonghung-do, an island in the mouth of the harbor. From there, they relayed intelligence back to the UNC. With the help of locals, Clark, gathered information about tides, beach composition, mudflats, and seawalls. A separate reconnaissance mission, codenamed Trudy Jackson, was mounted by the US military which dispatched Lieutenant Youn Joung of the Republic of Korea Navy and South Korean Army Colonel Ke In-Ju to Incheon to collect further intelligence on the area.[52]

The tides at Incheon have an average range of 29 feet (8.8 meters) and a maximum observed range of 36 feet (11 meters), making the tidal range there one of the largest in the world and the littoral maximum in all of Asia. Clark observed the tides at Inchon for two weeks and discovered that American tidal charts were inaccurate, but, fortunately, Japanese charts were quite good.[53] Detailed reports were provided on North Korean artillery positions and fortifications on the island of Wolmido, at Incheon, and on nearby islands. During the extensive periods of low tide they located and removed some North Korean naval mines, but, critically to the future success of the invasion, Clark reported that the North Koreans had not in fact systematically mined the channels.[54]

When the North Koreans discovered that the agents had landed on the islands near Incheon, they made multiple attacks, including an attempted raid on Yonghung-do with six junks. Clark mounted a machine gun on a sampan and sank the attacking junks.[55] In response, the North Koreans killed perhaps as many as 50 civilians for helping Clark.[56]