The Haijiu class submarine chasers are two (possibly four) modified versions of the Hainan class submarine chasers

Type 037 class submarine chaser

The Type 037 class submarine chaser, also known as the Hainan class, is a class of submarine chaser of the People's Republic of China's People's Liberation Army Navy, designed by China to replace the Soviet S.O.-1 class submarine chaser...

 (Type 037) of the People's Liberation Army Navy

People's Liberation Army Navy

The People's Liberation Army Navy is the naval branch of the People's Liberation Army , the military of the People's Republic of China. Until the early 1990s, the navy performed a subordinate role to the PLA Land Forces. Since then, it has undergone rapid modernisation...

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The main difference is that four ASW

Anti-submarine warfare

Anti-submarine warfare is a branch of naval warfare that uses surface warships, aircraft, or other submarines to find, track and deter, damage or destroy enemy submarines....

rocket launchers have replaced the original two ASW mortars. There is some disagreement over the type designation of this class, some sources claim it is Type 037I, while others claim it is Type 037 Mod (for modified or modernized).