China first received a single unit of Soviet Osa-class missile boat in January 1965, and four more in 1966 through 1967 and the last two in 1968. Eventually the Hudong Shipyard built the Chinese version as Type 021-class missile boat at a rate of ten boats per year with several different versions. Although majority of this class is being transferred to reserve, several dozens remain active and these active units are being rearmed with C-101 supersonic anti-ship missiles. These boats are effectively used in swarm missile attacks.