This prompted the development of ships designed to operate in such waters - the Zumwalt class destroyer and the littoral combat ships. Rubel has proposed redefining green water as those areas of ocean which are too dangerous for high-value units, requiring offensive power to be dispersed into smaller vessels such as submarines that can use stealth and other characteristics to survive.[2] Under his scheme brown water would be zones in which ocean-going units could not operate at all, including rivers, minefields, straits and other choke points.[2]