Abstract: To meet the transformational requirements of distributed maritime operations, the United States is accelerating the development of new combat capabilities centered on unmanned systems. However, the development pathways of maritime unmanned systems differ significantly across countries and regions. These differences are reflected not only in platform selection and technical configurations, but also in operational concepts, capability-generation models, and approaches to integrating unmanned systems into maritime forces. Focusing primarily on the United States, and incorporating the practical experience of Ukraine, Israel, Iran, and other countries and regions, this paper conducts a comparative analysis of the evolution of maritime unmanned systems and the divergence of development pathways worldwide. First, based on the development history, classification characteristics, and typical operational scenarios of U.S. unmanned surface vehicles (USVs) and unmanned underwater vehicles (UUVs), this paper constructs a three-dimensional autonomy assessment framework from the perspective of mission characteristics. The framework comprises environmental complexity, mission complexity, and the degree of human-machine interaction. Environmental complexity reflects the external conditions under which unmanned systems operate; mission complexity characterizes the difficulty and diversity of operational tasks; and the degree of human-machine interaction describes the extent of human involvement in supervision, decision-making, and control. Through this framework, the paper reveals the intrinsic coupling relationship among the size, mission profile, and autonomy level of unmanned maritime systems. Specifically, platform size is closely associated with mission scope, operational employment, and the level of autonomy required for effective mission execution. On this basis, the paper further analyzes the fundamental differences between manned and unmanned maritime systems from five dimensions: expendability, command and control, agility, human-machine teaming, and development philosophy. The framework is then applied to examine the development trends of unmanned maritime systems across different countries. The analysis identifies two dominant development pathways: a high-end, system-oriented pathway and a low-cost, mass-oriented pathway. The former emphasizes advanced capabilities, system integration, and a high degree of operational coordination, whereas the latter focuses on affordability, quantity, and scalable employment. Based on these findings, the paper proposes a hybrid development model that integrates the advantages of both pathways and reflects the potential convergence of future development trends. Finally, in light of China's strategic positioning and maritime security requirements, this paper discusses implications for pathway selection, intelligent communications, autonomous mission planning, and coordinated offensive and defensive operations. Future development trends are also examined from the perspective of system development and operational capability generation. The findings provide a theoretical reference for the systematic development of China's maritime unmanned systems and the generation of operational capabilities.