The authors have developed Souryu-I, Souryu-II and Souryu-III, connected crawler vehicles that can travel in rubble. These machines were developed for the purpose of finding survivors trapped inside collapsed buildings. However, when conducting experiments in post-disaster environments with Souryu-III, mechanical and control limitations have been identified. This led the authors to develop novel crawler units using crawler tracks strengthened with metal, and develop two improved models, called Souryu-IV (composed of three double-sided crawler bodies, a joint driving unit, a blade-spring joint mechanism, and cameras) and Souryu-V (composed of mono-tread-crawler bodies, elastic-rod-joint mechanisms, and cameras). The authors then conducted basic motion experiments and teleoperated control experiments on off-road fields with Souryu-IV and Souryu-V. Their high performance in experiments of urban rescue operations was confirmed. However, several problems were identified during the driving experiments, and are reported in this paper, as well as a few possible solutions to solve them. This paper describes Souryu-IV and Souryu-V, their mechanisms, their cameras, and the experiments to test their mobile performance. (c) 2008 Wiley Periodicals, Inc.