This paper presents the overview of a R&D project "Zipangu of the Sea", focusing on the sub-R&D project supervised by National Maritime Research Institute of Japan. Consisting of 7 sub-projects, main object of the Zipangu of the Sea project is the development of core technologies required for exploring, investigating, monitoring, protecting, and developing benthic mineral resources. The project is a collaborative R&D conducted by national institutes, universities, and private companies in Japan. The NMRI of Japan leads a sub-R&D project of developing the system and strategy for simultaneous deployment and operation of multiple AUVs. In this sub-project, AUVs play a leading role as a cutting-edge undersea probe. Supervised by an USV, multiple AUVs form a fully-autonomous undersea survey unit. In this paper, we introduce a new benthic resource survey system consisting of multiple AUVs and an USV being developed by R&D association led by NMRI. Key technologies as well as hardware elements consisting of our system are also overviewed.