A fleet, or naval fleet, is a large formation of warships, and the largest formation in any navy

Navy

A navy is the branch of a nation's armed forces principally designated for naval and amphibious warfare; namely, lake- or ocean-borne combat operations and related functions...

. A fleet at sea

Sea

A sea generally refers to a large body of salt water, but the term is used in other contexts as well. Most commonly, it means a large expanse of saline water connected with an ocean, and is commonly used as a synonym for ocean...

 is the direct equivalent of an army

Army

An army An army An army (from Latin arma "arms, weapons" via Old French armée, "armed" (feminine), in the broadest sense, is the land-based military of a nation or state. It may also include other branches of the military such as the air force via means of aviation corps...

 on land.

Fleets are usually, but not necessarily, permanent formations and are generally assigned to a particular ocean

Ocean

An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

 or sea

Sea

A sea generally refers to a large body of salt water, but the term is used in other contexts as well. Most commonly, it means a large expanse of saline water connected with an ocean, and is commonly used as a synonym for ocean...

. Most fleets are named after that ocean or sea, but the convention in the United States Navy

United States Navy

The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...

 is to use numbers.

A fleet is normally commanded by an Admiral

Admiral

Admiral is the rank, or part of the name of the ranks, of the highest naval officers. It is usually considered a full admiral and above vice admiral and below admiral of the fleet . It is usually abbreviated to "Adm" or "ADM"...

, who is often also a commander in chief, but many fleets have been or are commanded by Vice Admiral

Vice Admiral

Vice admiral is a senior naval rank of a three-star flag officer, which is equivalent to lieutenant general in the other uniformed services. A vice admiral is typically senior to a rear admiral and junior to an admiral...

s or even Rear Admiral

Rear Admiral

Rear admiral is a naval commissioned officer rank above that of a commodore and captain, and below that of a vice admiral. It is generally regarded as the lowest of the "admiral" ranks, which are also sometimes referred to as "flag officers" or "flag ranks"...

s. Most fleets are divided into several squadrons

Squadron (naval)

A squadron, or naval squadron, is a unit of 3-4 major warships, transport ships, submarines, or sometimes small craft that may be part of a larger task force or a fleet...

, each under a subordinate admiral. Those squadrons in turn are often divided into divisions. In the age of sail

Age of Sail

The Age of Sail was the period in which international trade and naval warfare were dominated by sailing ships, lasting from the 16th to the mid 19th century...

, fleets were divided into van, centre and rear squadrons, named after each squadron’s place in the line of battle

Line of battle

In naval warfare, the line of battle is a tactic in which the ships of the fleet form a line end to end. A primitive form had been used by the Portuguese under Vasco Da Gama in 1502 near Malabar against a Muslim fleet.,Maarten Tromp used it in the Action of 18 September 1639 while its first use in...

. In more modern times, the squadrons are typically composed of homogeneous groups of the same class of warship

Warship

A warship is a ship that is built and primarily intended for combat. Warships are usually built in a completely different way from merchant ships. As well as being armed, warships are designed to withstand damage and are usually faster and more maneuvrable than merchant ships...

, such as battleships or cruisers.

Since many smaller navies

Navy

A navy is the branch of a nation's armed forces principally designated for naval and amphibious warfare; namely, lake- or ocean-borne combat operations and related functions...

 only contain a single fleet, the term the fleet is often synonymous with the navy.

Multinational fleets are not uncommon in naval history. For example, several nations made up the Holy League

Holy League (Mediterranean)

The Holy League of 1571 was arranged by Pope St. Pius V and included almost all the major Catholic maritime states in the Mediterranean. It was intended to break the Ottoman Turks' control of the eastern Mediterranean Sea and was formally concluded on 25 May 1571...

 fleet

Battle of Lepanto order of battle

This is the order of battle during the Battle of Lepanto on 7 October 1571 in which the Holy League deployed 6 galleasses and 206 galleys, while the Ottoman forces numbered 216 galleys and 56 galliots.-The Fleet of the Holy League¹:...

 at the Battle of Lepanto

Battle of Lepanto (1571)

The Battle of Lepanto took place on 7 October 1571 when a fleet of the Holy League, a coalition of Catholic maritime states, decisively defeated the main fleet of the Ottoman Empire in five hours of fighting on the northern edge of the Gulf of Patras, off western Greece...

 in 1571. In modern times, NATO has formed standing combined fleets and operations from several national navies such as Operation Active Endeavour

Operation Active Endeavour

Operation Active Endeavour is a maritime operation of the North Atlantic Treaty Organization. It operates in the Mediterranean Sea and is designed to prevent the movement of terrorists or weapons of mass destruction. It has also collateral benefits in enhanced security of shipping in general...

.

See list of fleets for individual fleets.

The modern fleet

Modern fleets combine surface warships, submarines, support ships and ship-based aircraft to conduct naval operations at sea. Generally understood to be the blue water

Blue-water navy

The term blue-water navy is a colloquialism used to describe a maritime force capable of operating across the deep waters of open oceans. While what actually constitutes such a force remains undefined, there is a requirement for the ability to exercise sea control at wide ranges...

, or oceanic, green water

Green-water navy

A Green-Water Navy is a naval term that refers to a naval force whose power projection capability is regional in nature. This is a relatively new terminology, as earlier non blue-water navies used to be collectively referred to as brown-water navy....

 or littoral

Littoral

The littoral zone is that part of a sea, lake or river that is close to the shore. In coastal environments the littoral zone extends from the high water mark, which is rarely inundated, to shoreline areas that are permanently submerged. It always includes this intertidal zone and is often used to...

 versus the brown water

Brown-water navy

Brown-water navy is a term that originated in the United States Navy, referring to the small gunboats and patrol boats used in rivers, along with some of the larger ships that supported them as "mother ships," from which they operated...

 or coastal/riverine forces. The fleets of larger navies are usually divided into smaller numbered or named fleets based on geographic operating areas or on administrative groupings of same type ships.

Modern fleets are usually administrative units. Typically individual task force

Task force

A task force is a unit or formation established to work on a single defined task or activity. Originally introduced by the United States Navy, the term has now caught on for general usage and is a standard part of NATO terminology...

s are formed to conduct specific operations.