Blue-water navy
Attributes: In public discourse, blue-water capability is identified with the operation of capital ships such as battleships, battlecruisers, aircraft carriers, and nuclear submarines. For instance, during the debate in the 1970s whether Australia should replace HMAS Melbourne, a former chief of navy claimed that if Australia did not replace her last aircraft carrier, she "would no longer have a blue-water navy". In the end Australia did not buy a new carrier, but former Parliamentary defence advisor Gary Brown could still claim in 2004 that her navy remained "an effective blue-water force". The Soviet Navy towards the end of the Cold War is another example of a blue-water navy that had minimal carrier aviation, relying instead on submarines, missile-carrying surface ships, and long-range bombers based on land.
A blue-water navy implies force protection from underwater warfare, surface warfare, and aerial warfare threats and a sustainable logistic reach, allowing a persistent presence at long range. A hallmark of a true blue-water navy is the ability to conduct replenishment at sea (RAS), and the commissioning of underway replenishment ships is a strong sign of a navy's blue-water ambitions. While a blue-water navy can project sea control power into another nation's littoral waters, it remains susceptible to threats from less capable forces (asymmetric warfare). Maintenance and logistics at range have high costs, and there might be a saturation advantage over a deployed force through the use of land-based air or surface-to-surface missile assets, diesel-electric submarines, or asymmetric tactics with fast attack craft (FAC). An example of this vulnerability was the October 2000 USS Cole bombing in Aden.
The term 'blue-water navy' should not be confused with the capability of an individual ship. For example, vessels of a green-water navy can often operate in blue water for short periods of time. A number of nations have extensive maritime assets but lack the capability to maintain the required sustainable logistic reach. Some of them join coalition task groups in blue-water deployments such as anti-piracy patrols off Somalia.

Definitions: According to a dictionary definition, blue-water capability refers to an oceangoing fleet able to operate on the high seas far from its nation's home ports. Some operate throughout the world.
In their 2012 publication, "Sea Power and the Asia-Pacific",  professors Geoffrey Till and Patrick C. Bratton outlined what they termed as "concise criteria" with regard to the definitions of brown-, green- and blue-water navies. Quote; "...a brown-water navy standing for a navy capable of defending its coastal zones, a green-water navy for a navy competent to operate in regional sea and finally [a] blue-water navy described as a navy with capability to operate across the deep waters." They go on to say that even with such a definition and understanding of naval hierarchy, it is still "ambiguous". For example, while France and the United States may be considered blue-water navies, he states that the "operational capability and geographic reach of both navies are definitely different."
Another definition states that 'brown-water' refers to the littoral areas within 100 nautical miles of the coastline. 'Green-water' begins from 100 nautical miles out to the next major land formation, while 'blue-water' is the ability to project force out to at least 1,500 nautical miles beyond the coast. Traditionally a distinction used to be made between a coastal brown-water navy operating in the littoral zone to 200 nautical miles (or 370 kilometres) and an oceangoing blue-water navy. However, the United States Navy created a new term, green-water navy, to replace the term 'brown-water navy' in US Navy parlance. Today, a brown-water navy has come to be known as a predominantly riverine and littoral force.
Despite the above, however, there is no agreed definition of the term.

Classification and naval hierarchy: There have been many attempts by naval scholars and other authorities to classify world navies, including; Michael Morris, British naval historians Eric Grove and Professor Geoffrey Till, French strategist Hervé Coutau-Bégarie and professors Daniel Todd and Michael Lindberg.  All identify basic common criteria for gauging the capability of navies, such as; total displacement and number of ships; modernity and power of weapons and systems; logistical and geographic reach with capacity for sustained operations; and the professional qualifications/disposition of sailors.

The table below shows the world naval hierarchy according to the classification system by professors Daniel Todd and Michael Lindberg. Their system originates from 1996 and outlines ten ranks, distinguished by capability. Since then it has been used by various other experts to illustrate the subject. According to Todd and Lindberg, a "blue-water navy" is one that can project any sort of power beyond its own territorial waters. However they used the principle of loss of strength gradient and other criteria to distinguish navies by capability under the four "blue-water" ranks. The six ranks of "Non blue-water navies" can be further broken down into "green-water" and "brown-water navies", and according to Todd and Lindberg, these are navies only capable of operating as coastal defence forces, coast guards or riverine forces.

Overseas basing: Historically, and to present day, blue-water navies have tended to establish overseas bases to extend the reach of supply lines, provide repair facilities and enhance the "effective striking power" of a fleet beyond the capabilities provided by the nation's homeports. Generally, these overseas bases are located within areas where potential conflicts or threats to the nation's interests may arise. For example, since World War II the Royal Navy and later the United States Navy have continued to base forces in Bahrain for operations in the Persian Gulf. The military importance and value of overseas basing is primarily dependent on geographical location. A base located at choke points in narrow or enclosed seas can be of high value, especially if  positioned near, or within striking distance of an enemy's sea lines of communications. However advanced operating bases (or forward operating bases) can be equally as valuable. Naval Station Pearl Harbor acts as a "gateway" for the US Navy to "operate forward" in the Pacific Ocean.

Examples: These are examples of navies that have been described by various defense experts or academics as being blue-water navies. Some have successfully used their blue-water capabilities to exercise control on the high seas and from there have projected power into other nations' littoral waters. However, there is no agreed upon definition among authorities as to what constitutes a blue-water navy.

China: The People's Liberation Army Navy (PLAN) is subject to a variety of assessments regarding its capabilities. China's ambition towards blue-water capability received much attention, particularly from the United States Congress and Department of Defense, with both acknowledging that China's primary aim was to project power in the First and Second island chains. In a 2013 report to Congress, defense experts also asserted that over the coming decades, China would gain the capability to project power across the globe – similar to Britain's 1982 Falklands War. In addition, there were those who thought China already had a blue-water navy, such as British naval historian and professor Geoffrey Till, and also, Professor David Shambaugh who believed that the PLAN had transitioned from a green-water navy to that of a "limited" blue-water navy. According to Todd and Lindberg's classification system, the PLAN was a rank four "regional power projection navy".
Since 2008, the PLAN has conducted anti-piracy missions in the Gulf of Aden on a continuous basis.

France: The French Navy is recognised as being a blue-water navy by various experts and academics.[A] According to professors Daniel Todd and Michael Lindberg, the French Navy is a rank two "limited global-reach power projection navy".
The navy operates a single nuclear-powered aircraft carrier (Charles de Gaulle) which forms the centrepiece of the  Navy's principal expeditionary task group (known as the Aeronaval Group). In addition to this, the navy maintains a secondary Amphibious Group (known as Le Groupe Amphibie) based around the Mistral-class amphibious assault ships. Both these formations are part of the Force d'action navale (or Naval Action Force). The 'Forces sous-marines' operates four nuclear-powered ballistic missile submarines and six nuclear-powered fleet submarines. France retains a network of overseas naval facilities around the world; from Fort de France in the Caribbean, to Le Port, Réunion in the Indian Ocean, Papeete in the Pacific and in several other parts of the world too, including the Gulf, South Atlantic and the Western Pacific.
The navy's operational duties include the protection of French interests abroad and the security of the nation's many overseas departments and territories, as such the Navy undertakes a number of standing commitments worldwide.

India: The Indian Navy is unique among Asian navies due to its long experience in carrier power projection since 1961. This, according to Dr. George J. Gilboy and political scientist Eric Heginbotham, gives the Indian Navy the "leading power projection capability in the region". The Indian Navy is also the only Asian navy considered to be a rank three "multi-regional power projection navy" per Todd and Lindberg's classification system. In his discussion paper for Consultancy Africa Intelligence, Greg Ryan asserts that in recent years, the Indian Navy has emerged as a "global power in the blue water sense".