Shiretoko-class patrol vessel

Shiretoko class patrol vessel (しれとこ型巡視船) is a class of PL type patrol vessels of the Japan Coast Guard (JCG; former Maritime Safety Agency, MSA). PL stands for "Patrol vessel Large", and the class name "Shiretoko" is named after Shiretoko, the northeastern area of the island of Hokkaidō, Japan

In 1977, Act on Territorial Waters and Contiguous Water Area and the Act on Temporary Measures Concerning Fishery Waters was confirmed by the National Diet of Japan to adapt for the UNCLOS III. As a direct result of these acts, the coverage area of the MSA was dramatically extended, so the update of their equipment became a thing of the urgent. In consequence of these situations, the MSA had put some series of patrol vessels into commission from late 1970s to early 1980s.

This class was one of these series, planned to form the main fleet in the high-endurance mission. This class was designed as the enlarged and mass-production variant of the Daiou-class, preceding large patrol vessels. Early-batch of this class equipped with one Bofors 40 mm L/60 gun like the Daiou-class, but latter-batch had changed their weapon to the new Oerlikon KDC 35mm gun. And later, ships of the early-batch converted their weapon to the JM61-M 20mm gun.