In naval warfare, blue water operations take place either in the open ocean, or, as a secondary aspect, as transit to shallower-water operational areas, perhaps facing detection or attack in the transit. A vessel for this function obviously will need long range, high speed, and long-range sensors and weapons.
Blue water was characteristic both of the Cold War and Second World War. In today's geopolitical environment, "green water" of coastal areas of ocean, and "brown water" on inland waterways, jointly forming the "littoral", create new challeges for modern ships in shallow water of the littoral .
A blue water submarine, for example, may be limited in its ability to operate in constrained waters such as the Persian Gulf or Shatt-el-Arab. An aircraft carrier is very vulnerable here, but is extremely potent when operating from deeper waters farther from coast defenses.
The U.S., for example, capped its Seawolf-class submarine production, vessels intended to dominate the blue water, for the more flexible and cheaper Virginia-class. Its previous generation, the Los Angeles-class, was optimized for blue water operations of a specific type: being part of a Carrier Strike Group with the speed to operate jointly with fast surface vessels.
- National Academy of Sciences Commission on Geosciences, Environment and Resources (CGER) (April 29-May 2, 1991), Chapter 9: Measurement and Signals Intelligence, Naval Amphibious Base, Little Creek, Virginia: National Academies Press