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.

[3] Like preceding PLHs with a single helicopter, they have a long forecastle, but hull designs have changed significantly.

Fin stabilizers were retained, but antiroll tanks were omitted as their hull was so big that they were unnecessary.

[1][4] Because they operate far away from the mainland Japan, the command and control capability is strengthened than preceding PLHs.