Japanese Navy in the Persian Gulf, 1990

From Geography and Japan's Strategic Choices: From Seclusion to Internationalization, by Peter J. Woolley (Potomac Books, 2005), Kindle p. 143:

Japan’s final contributions [to the 1990 war on Iraq] totaled $13 billion. Only three countries had spent more: Kuwait, Saudi Arabia, and the United States. Japan had also frozen Iraqi assets and embargoed Iraqi oil. And its initial financial commitment in August of 1990 beat Germany’s announcement by ten days. Nonetheless, it was, as critics had charged, largely “checkbook diplomacy,” which incurred no substantial risk to the Japanese people.

The deployment of minesweepers, even after the hostilities were over, was a signal departure from the policies of the past. [Prime Minister] Kaifu was forced to deploy them without the aid of any legislation from the Diet, claiming that they were not going to a war zone but would be in international waters, merely clearing obstacles for international shipping. It would take some time for the Japanese public and the parliament to come around. The LDP leaders believed, however, that if the minesweeping mission was successful, the public would support a substantial change in defense policy and allow the SDF to be deployed on other missions.

Six ships and a crew of 511 made the trip to the Persian Gulf. The vessels were small but relatively modern. The largest of the six was a ship-tender of 8,000 tons. The mine warfare ships were just 510 tons and did indeed have wooden hulls. But then, recent minesweepers all had wooden hulls as a precaution against magnetic devices.

The minesweepers probably would not have been more useful had they been sent sooner. Before the UN deadline expired, little minesweeping was done because the allied commander did not want to risk touching off an early confrontation. After the deadline expired, minesweeping was mainly to give the appearance that the allies might make an amphibious assault on the Kuwaiti coast. Japan might have joined the allied minesweepers somewhat sooner but even its arrival in late May was useful. Iraq had dropped over a thousand mines in a long swath off the Kuwaiti coast. It took more than two dozen minesweepers and ten support ships from eight different countries over four months to clean up the mess.

According to a map in the Japanese Maritime Self-Defense Force Museum in Kure (near Hiroshima), Japan itself laid 55,347 mines to defend its perimeter: 15,474 along the Tokai and southwestern island chain, 14,927 in the northern Honshu and Shikoku regions, 10,012 along the coast of Kyushu, 7,640 along the south coast of Korea and across the Yellow Sea, and 7,294 around Taiwan.

The same map shows that the U.S. laid most of its 10,703 naval mines in the Inland Sea and along the Japan Sea coast (to destroy economic supply routes). When we visited the museum in 2015, a total of 297 American naval mines from World War Two remained unaccounted for. Mine disposal efforts continue to this day.