The original one-off design was by an American company, the H-3 group, the design was for a 245-ton boat, equipped with Harpoon SSMs, OTO Melara 76 mm guns, gas turbine engines and waterjet propulsion. However, this specifications was too complicated for China, and a major redesign was begun, resulting in a boat with C-801 SSMs, diesel engines and propellers instead. The OTO Melara 76mm gun was retained in the revised design, called in 1988 the EH-3D (and in 1996 the 520T), but failed to survive the cooling of relations with the West following the Tiananmen Square protests of 1989 and the resulting end of Western participation in Chinese military projects.