Mizuho (PLH-21) is the lead ship of Mizuho-class patrol vessel of Japanese Coast Guard.

In response to this Convention, Japan and the United States shared the search and rescue activities on the Pacific Ocean by concluding "Agreement on search and rescue at sea between the Japanese government and the United States government" (Japan-US SAR agreement).

At the end of 1980, certain large scale marine accidents occurred, and in March 1981 accidents of large tankers and cargo ships occurred in the Malacca Straits, and the development of wide area patrol system became an urgent task.

After that, with the commissioning of Shikishima, she was reassigned to the Nagoya Coast Guard (Fourth Division) on 16 December 1991.

[4] In addition, on 5 July 2019, with the commissioning of the new Mizuho, he was reassigned to the Maizuru Maritime Security Department (8th Regional Coast Guard), and at this time the name was changed to Fusō.