Smaller tug-type vessels intended for salvage and towing duties, primarily in support of submarines. Could also operate as general salvage ships. The existence of the 4th unit is uncertain. Have also been used as electronic surveillance ships. Zhonghua SY, Shanghai.
Some reports indicate one unit is laid up in reserve.
The sole 'Dadao' is of slightly different dimensions. Additional 'Dadongs' are being built. Equipped for heavy towing and firefighting. Up to 17 are in service. Some sources list four units in service, but others list up to 19 units.