Many marine mammal species, such as different kinds of whales and dolphins, live together in groups. Although having no nice eyesight, they can accomplish cooperative foraging, inter-communication and group sailing very efficiently and accurately only depending on their sound. Generally, present interception systems almost always classify biological signals as ocean noise and try to filter them out. In addition, the covertness and security are very important for many military underwater platforms (MUPs) and their formations. Based on above classification fact and covert communication demand, this article designs a basic bio-inspired camouflage communication frame (BBICCF) for secure underwater communication among military underwater platforms based on the killer whale sound. According to characteristics of the killer whales' original call pulse trains, the original long duration call pulses (whistles and pulsed calls) are utilized as communication address codes for each MUP so as to provide disguised communication addressing support for interconnection among multiple MUPs in the same formation, and the original short duration call pulses (clicks) are used as other communication codes, so as to construct BBICCF for highly camouflaged conveying communication information. A simple and effective time-frequency (TF) contour extraction method is proposed to achieve the accurate extraction of the TF contour of the fundamental frequency of whistles and pulsed calls of killer whales for efficient classification and decoding of address codes. Next, this article provides some extensions and applications about how to let the BBICCF to be applied in conventional communication networks for MUP formation. Finally, simulation results show the effectiveness and concealment ability of designed BBICCF. INDEX TERMS Secure communication network, underwater communications, whale sound, underwater formation. I. INTRODUCTION With the development of technology, more and more autonomous underwater vehicle (AUV), glider and varieties of formations composed of them are used in many military application scenarios from surveillance and anti-submarine, The associate editor coordinating the review of this manuscript and approving it for publication was Xingwang Li. to reconnaissance and mine detection etc. [1]-[3]. Compared with single MUP, the formation composed of multiple MUPs can accomplish more complex, wider range, and more reliable military tasks [4], [5], just as multitudinous group animals in nature, such as whales, swarms, wolf packs etc.. However, the accomplishment of collaborative tasks among the MUPs, such as cooperative localization, sailing of multiple platforms, interaction of the order/data among multiple
