thumb|right|350px|The four kinds of navigable water in the [[Gulf of Mexico.]]
Maritime geography is a collection of terms used by naval military units to loosely define three maritime regions: brown water, green water, and blue water.
Definitions
The elements of maritime geography are loosely defined and their meanings have changed throughout history. The USA's 2010 Naval Operations Concept defines blue water as "the open ocean", green water as "coastal waters, ports and harbors", and brown water as "navigable rivers and their estuaries". Robert Rubel of the US Naval War College includes bays in his definition of brown water, and in the past US military commentators have extended brown water out to from shore.
During the Cold War, green water denoted those areas of ocean in which naval forces might encounter land-based aircraft and brown water, land-based artillery. This distinction disappeared as increasing threats in coastal waters forced the amphibious ships further offshore, delivering assaults by helicopter and tiltrotor from over the horizon. 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.
See also
- Littoral zone