Looking across the world today, the ocean is increasingly prominent as a critical domain for global resource development, economic growth, and strategic competition. The United States Unmanned Systems Integrated Roadmap (2021) proposed the construction of a cross-domain unmanned combat system. The European Union, through its European Defence Fund, prioritized support for the development of underwater autonomous systems. China is a major land and maritime nation, whose 14th Five-Year Plan also identifies unmanned systems as a development priority. Against this backdrop, MUSs, as a key component of cross-domain clusters, provide technical support for developing marine resources, and maintaining maritime security. Their capabilities include efficient networking in complex environments, precise detection, and intelligent control. However, constrained by the current technological development, MUSs still face multiple bottlenecks. These include communication reliability, detection accuracy, energy consumption optimization, and intelligent collaboration. In the future, in-depth research should target key technological shortcomings. Methodologies need continuous refinement. This chapter outlines several important yet unresolved issues in the detection-networking-control coordination of MUSs. It also suggests future directions worthy of further exploration.