I. Introduction
With the increasing complexity of underwater operations, UUVs swarm operation has become a major trend. The key to ensure the safe completion of UUVs swarm operation depends on the UUVs swarm threat assessment and decision making system. The concept of threat assessment originated from the Joint Directors of Laboratories(JDL). The famous JDL data fusion model proposed by the data fusion group under JDL [1]. The model was originally set in battlefield confrontation. It proposed a multi-level structure that guides the fusion of multiple information in the battlefield scenario. With the development of the model, it is no longer limited to military applications, and the definition of each level is gradually refined [2]–[5].