A navy is the branch of a country's military forces principally designated for naval warfare and amphibious warfare namely lake- or ocean-borne combat operations and related functions. It includes operations conducted by surface ships, amphibious ships, submarines, and seaborne aviation, as well as ancillary support, communications, training, and other fields; recent developments have included space related operations. The strategic offensive role of a Navy is projection of force into areas beyond a country's shores (for example, to protect sea-lanes, ferry troops, or attack other navies, ports, or shore installations). The strategic defensive purpose of a Navy is to frustrate sea-borne projection-of-force by enemies. The strategic task of the navy also may incorporate nuclear deterrence by use of nuclear missiles.
Naval warfare developed when humans first fought from water-borne vessels. Prior to the introduction of the cannon and ships with sufficient capacity to carry the large guns, navy warfare primarily involved ramming and boarding actions. In the time of ancient Greece and the Roman Empire, naval warfare centered on long, narrow vessels powered by banks of oarsmen (such as triremes and quinqueremes) designed to ram and sink enemy vessels or come alongside the enemy Nublets so its occupants could be attacked hand-to-hand. Naval warfare continued in this vein through the Middle Ages until cannon became commonplace and capable of being reloaded quickly enough to be reused in the same battle. The Chola Dynasty of medieval India was known as a one of the greatest naval powers of its time in the Indian Ocean. In ancient China, large naval battles were known since the Qin Dynasty (also see Battle of Red Cliffs, 208), employing the war junk during the Han Dynasty. However, China's first official standing navy was not established until the Southern Song Dynasty in the 12th century, a time when gunpowder was a revolutionary new application to warfare
The mass and deck space required to carry a large number of cannon made oar-based propulsion impossible and ships came to rely primarily on sails. Warships were designed to carry increasing numbers of cannon and naval tactics evolved to bring a ship's firepower to bear in a broadside, with ships-of-the-line arranged in a line of battle.
The development of large capacity, sail-powered ships carrying cannon led to a rapid expansion of European navies, especially the Spanish and Portuguese navies which dominated in the 16th and early 17th centuries, and ultimately helped propel the age of exploration and colonialism.The repulsion of the Spanish Armada (1588) by the English fleet revolutionized naval warfare by the success of a guns-only strategy and caused a major overhaul of the Spanish navy, partly along English lines, which resulted in even greater dominance by the Spanish. From the beginning of the 17th century the Dutch cannibalized the Portuguese Empire in the East and, with the immense wealth gained, challenged Spanish hegemony at sea. From the 1620s, Dutch raiders seriously troubled Spanish shipping and, after a number of battles which went both ways, the Dutch Navy finally broke the long dominance of the Spanish Navy in the Battle of the Downs (1639).
England emerged as a major naval power in the mid-17th century in the first Anglo-Dutch war with a technical victory but successive decisive Dutch victories in the second and third Anglo-Dutch Wars confirmed the Dutch mastery of the seas during the Dutch Golden Age, financed by the expansion of the Dutch Empire. The French Navy won some important victories near the end of the 17th century but a focus upon land forces led to the French Navy's relative neglect, which allowed the Royal Navy to emerge with an ever-growing advantage in size and quality, especially in tactics and experience, from 1695. Throughout the 18th century the Royal Navy gradually gained ascendancy over the French Navy, with victories in the War of Spanish Succession (1701-1714), inconclusive battles in the War of Austrian Succession (1740-1748), victories in the Seven Years' War (1754-1763), a partial reversal during the American War of Independence (1775-1783), and consolidation into uncontested supremacy during the 19th century from the Battle of Trafalgar in 1805. These conflicts saw the development and refinement of tactics which came to be called the line of battle.
The next stage in the evolution of naval warfare was the introduction of metal plating along the hull sides. The increased mass required steam-powered engines, resulting in an arms race between armor and weapon thickness and firepower. The first armored vessels, the French FS Gloire and British HMS Warrior, made wooden vessels obsolete. Another significant improvement came with the invention of the rotating turrets, which allowed the guns to be aimed independently of ship movement. The battle between the CSS Virginia and the USS Monitor during the American Civil War is often cited as the beginning of this age of maritime conflict. A further step change in naval firepower occurred when the United Kingdom launched HMS Dreadnought, but naval tactics still emphasized the line of battle.
The first practical military submarines were developed in the late 19th century and by the end of World War I had proven to be a powerful arm of naval warfare. During World War II the German Navy's submarine fleet of U-boats almost starved the United Kingdom into submission and inflicted tremendous losses on US coastal shipping. The German battleship Tirpitz, a sister ship of the Bismarck, was almost put out of action by miniature submarines known as X-Craft. The X-Craft severely damaged her and kept her in port for some months.
A major paradigm shift in naval warfare occurred with the introduction of the aircraft carrier. First at Taranto in 1940 and then in Pearl Harbor in 1941, the carrier demonstrated its ability to strike decisively at enemy ships out of sight and range of surface vessels. The Battle of Leyte Gulf (1944) was arguably the largest naval battle in history; it was also the last battle in which battleships played a significant role. By the end of World War II, the carrier had become the dominant force of naval warfare.
World War II also saw the United States become by far the largest Naval power in the world with over 70% of the world's total numbers and total tonnage of naval vessels of 1000 tons or greater. Throughout the rest of the 20th century The United States Navy would maintain a tonnage greater than that of the next 17 largest navies combined.
Historically a national navy operates from one or more bases that are maintained by the country or an ally. The base is a port that is specialized in naval operations, and often includes housing for off-shore crew, an arsenal depot for munitions, docks for the vessels, and various repair facilities. During times of war temporary bases may be constructed in closer proximity to strategic locations, as it is advantageous in terms of patrols and station-keeping. Nations with historically strong naval forces have found it advantageous to obtain basing rights in areas of strategic interest.
Navy ships normally operate with a group, which may be a small squadron of comparable ships, or a larger naval fleet of various specialized ships. The commander of a fleet travels in the flag ship, which is usually the most powerful vessel in the group. Prior to the invention of radio, commands from the flag ship were communicated by means of flags. At night signal lamps could be used for a similar purpose. Later these were replaced by the radio transmitter, or the flashing light when radio silence was needed.
A "blue water navy" is designed to operate far from the coastal waters of its home nation. These are ships capable of maintaining station for long periods of time in deep ocean, and will have a long logistical tail for their support. Many are also nuclear powered to save having to refuel. By contrast a "brown water navy" operates in the coastal periphery and along inland waterways, where larger ocean-going naval vessels can not readily enter. Regional powers may maintain a "green water navy" as a means of localized force projection. Blue water fleets may require specialized vessels, such as mine sweepers, when operating in the littoral regions along the coast.
A basic tradition is that all ships commissioned in a navy are referred to as ships rather than vessels. The prefix on a ship's name indicates that it is a commissioned ship. For example, USS is an acronym which expands to United States Ship; in the Royal Navy, HMS expands to Her Majesty's Ship (or when a King reigns, His Majesty's Ship), and so forth.
An important tradition on board British naval vessels (and later those of the U.S. and other nations) has been the ship's bell. This was historically used to mark the passage of time on board a vessel, including the duration of four-hour watches. They were also employed as warning devices in heavy fog, and for alarms and ceremonies. The bell was originally kept polished first by the ship's cook, then later by a person belonging to that division of the ship's personnel.
Another important tradition is that of Piping someone aboard the ship. This was originally used to give orders on warships when shouted orders could not have been heard. The piping was done by the ship's boatswain and therefore the instrument is known as the boatswain's Pipe. The two tones it gives and the number of blasts given off, signify the order given. It is also used in a ceremonial way, i.e., to "pipe" someone aboard the ship - usually captains, including the ship's captain, and more senior officers.
By European tradition, ships have been referred to as a "she". However, it was long considered bad luck to permit women to sail on board naval vessels. To do so would invite a terrible storm that would wreck the ship. The only women that were welcomed on board were figureheads mounted on the prow of the ship. In spite of these views, some women did serve on board naval vessels, usually as wives of crewmembers.
Even today, despite their acceptance in many areas of naval service, women are still not permitted to serve on board U.S. submarines. The major reasons cited by the U.S. Navy are the extended duty tours and close conditions which afford almost no privacy.  The UK Royal Navy has similar restrictions. Australia, Canada, Spain and Norway have opened submarine service to women sailors, however. 
By ancient tradition, corpses on board naval vessels were buried at sea. In the past this involved sewing the body up in a shroud that had a weight at one end, often a cannonball. (During the age of sail, the final stitch was placed through the nose of the victim, just to make sure they were really dead.) The body was then placed on a pivoting table attached to the outer hull, and shrouded by a national ensign. After a solemn ceremony, the board was tilted and the body dropped into the deep. Later ceremonies employed the casket or crematory urn.
The custom of firing cannon salutes originated in the British Royal Navy. When a cannon is fired, it partially disarms the ship, so firing a cannon for no combat reason showed respect and trust. The British, as the dominant naval power, compelled the ships of weaker nations to make the first salute. As the tradition evolved, the number of cannon fired became an indication of the rank of the official being saluted.
 Naval organization
 Navy ships
Historically, navy ships were primarily intended for warfare. They were designed to withstand damage and to inflict the same, but only carried munitions and supplies for the voyage (rather than merchant cargo). Often, other ships which were not built specifically for warfare, such as the galleon or the armed merchant ships in World War II, did carry armaments. In more recent times, navy ships have become more specialized and have included supply ships, troop transports, repair ships, oil tankers and other logistics support ships as well as combat ships. So long as they are commissioned, however, they are all "ships".
Modern navy combat ships are generally divided into seven main categories: aircraft carriers, cruisers, destroyers, frigates, corvettes, submarines, and amphibious assault ships. There are also support and auxiliary ships, including the minesweeper, patrol boat, and tender. During the age of sail, the ship categories were divided into the ship of the line, frigate, and sloop-of-war.
Today ships are significantly faster than in former times, thanks to much improved propulsion systems. Also, the efficiency of the engines has improved a lot, in terms of fuel, and of how many sailors it takes to operate them. In World War II, ships needed to refuel very often. However, today ships can go on very long journeys without refueling. Also, in World War II, the engine room needed about a dozen sailors to work the many engines, however, today, only about 4-5 are needed (depending on the class of the ship). Today, naval strike groups on longer missions are always followed by a range of support and replenishment ships supplying them with anything from fuel and munitions, to medical treatment and postal services. This allows strike groups and combat ships to remain at sea for several months at a time.
 Navy boats
Many people make the mistake of calling a ship a "boat". The term "boat" refers to small craft limited in their use by size and usually not capable of making independent voyages of any length on the high seas. The old navy adage to differentiate between ships and boats is that boats are capable of being carried by ships. (Submarines by this rule are ships rather than boats, but are customarily referred to as boats reflecting their previous smaller size.) The Navy uses thousands of boats, ranging from 9-foot dinghies to 135-foot landing craft. They are powered by either diesels, out-board gasoline motors, or waterjets. Most boats are built of aluminum, fiberglass, or steel. Newer Navy boats are designed and built using the International System of units (also known as SI or metric), but older craft were designed using the English units system (feet, inches etc.)
Standard Boats A standard boat is a small craft carried aboard a ship to perform various tasks and evolutions.
Landing Craft These boats, carried by various amphibious ships, are designed to carry troops, vehicles, or cargo from ship to shore under combat conditions, to unload, to retract from beach, and to return to the ship. They are especially rugged, with powerful engines, and they are armed. They are usually referred to by their designations such as LCPL (landing craft, personnel) LCM (landing craft mechanized) or LCU (landing craft, utility) rather than by full name. The most common in today's Navy are the LCMs. there are two types of LCMs. Both types have a power operated bow ramp, a cargo well, twin engines, and after structures that house enginerooms, pilot houses, and stowage compartments. The larger version, designated LCM-8 and often called "mike 8", is 74 feet long, has a 21-foot beam, and is capable of carrying a heavy tank or 60 tons of cargo. The LCM-6 ("mike 6") is 56 feet long, has a 14-foot beam and a cargo capacity of 34 tons.
Landing Craft, Air Cushioned Known as LCAC also most commonly called a hover craft. Floats on a cushion of air that allows travel over water and land. It can deliver troops, equipment, and supplies. They are 81 feet long and carry a load more than 70 tons. Powered by four gas turbine engines, they are capable of speeds as high as 50 knots.
Work Boats(WB) There are two types of WBs, the 35 foot and the 15 meter (or 50 foot). The 35 foot WB is a twin screw craft with a forward cargo well and a bow ramp. The 35 foot WB is normally carried on board salvage ships and is used to assist ships in salvage operations, underwater exploration,coastal survey, repair of other craft, and cargo transport between ship to shore. A portable "A frame" is used to assist with cargo handling. The 15 meter (50 foot) WB is a twin screw craft with steel hull construction and is a shallow draft craft cargo carrier. The 15 meter (50 foot) WB is intended for general purpose missions and transportation of cargo. the craft has a pilot house aft and forward cargo well deck.
Rigid hull Inflatable Boats Known as the RHIB they are versatile boats designed for service as a standard ship's boat. The seven meter (24 foot) RHIB is a turbocharged, diesel powered craft with a glass reinforced plastic (GRP) hull. The hull form is a combination of a rigid planing hull with an inflatable tube. The craft are manned by three man crew and are provided with a canvas canopy forward.
Personnel Boats (PE) These are fast, V bottomed, diesel powered boats with enclosed spaces specifically designed to transport officers, although smaller types are used for shore party boats, lifeboats, and mail boats. They come in 8,10, and 12 meter (26,33, and 40 foot) lengths. The 8 meter (26 foot) boats have one enclosed cabin. The 10 and 12 meter (33 and 40 foot) boats have enclosed cabins forward and aft, and open cockpits amidships where coxswains steer by wheel. Those designed for officers are painted haze gray with white cabins. Those assigned for use by commanding officers, chief of staff, and squadron, patrol, or division commanders are called gigs and have a red stripe added just above the waterline. Personnel boats assigned to flag officers (admirals) are called barges. They have black hulls and a white stripes just above the waterline.
Utility Boats These boats, varying in length from 18 feet to 15 meters (50 feet) are mainly cargo and personnel carrier or heavy duty work boats. Many have been modified for survey work, tending divers, and minesweeping operations. In ideal weather, a 15 meter(50 foot) UB will carry 146 people, plus crew. Utility boats are open boats, though many of the larger ones are provided with canvas canopies. The smaller utility boats are powered by outboard engines. The larger boats have diesel engines.
Punts These are open square enders, 14 feet long. They are either rowed or sculled, and are generally used in port by side cleaners.
Special Boats These boats, used by shore stations and for special missions, are not normally carried aboard ships a are the standard boats discussed above. They include line handling boats, buoy boats, aircraft rescue boats, torpedo retrievers, explosive ordnance disposal craft, utility boats, dive boats, targets, and various patrol boats. Many standard boats have been modified for special service.
Mark V Special operations craft (SOC) This craft is also used for insertion and extraction of special warfare personnel. The craft is 82 feet long, and has twain diesel engines driving waterjets. The craft is capable of speeds in excess of 50 knots and is air deployable.
Patrol Boats, River (PBR) This is a 31 foot, 25 knots, twin diesel boats with a fiberglass hull and waterjet pump propulsion that permits it to operate in 15 inches of water. The PBR is highly maneuverable and can reverse course in its own length. It carries radar, communications equipment, and machine guns
 Navy units
Naval forces are typically arranged into units based on the number of ships included, a single ship being the smallest operational unit. Ships may be combined into squadrons or flotillas, which may be formed into fleets. The largest unit size may be the whole Navy or Admiralty.
 Naval ranks
Typical ranks for commissioned officers include the following, in ascending order (Commonwealth ranks are listed first on each line):
- Acting Sub-Lieutenant / Ensign / Corvette Lieutenant
- Sub Lieutenant / Lieutenant Junior Grade / Frigate Lieutenant
- Lieutenant / Ship-of-the-Line Lieutenant / Captain Lieutenant
- Lieutenant Commander / Corvette Captain
- Commander / Frigate Captain
- Captain / Ship-of-the-Line Captain
- Commodore / Flotilla Admiral (in USA only: Rear Admiral (lower half))
- Rear Admiral (in USA only: Rear Admiral (upper half))
- Vice Admiral
- Fleet Admiral or Admiral of the Fleet or Grand Admiral
"Flag officers" include any rank that includes the word "admiral" (or commodore), and are generally in command of a battle group or similar flotilla of ships, rather than a single ship or aspect of a ship. However, commodores can also be temporary positions. For example, during World War II, a Navy captain was assigned duty as a convoy commodore, which meant that he was still a captain, but in charge of all the merchant vessels in the convoy. The most senior rank employed by a navy will tend to vary depending on the size of the navy and whether it is wartime or peacetime, for example, few people have ever held the rank of Fleet Admiral in the U.S. Navy, the chief of the Royal Australian Navy holds the rank of Vice Admiral, and the chief of the Irish Naval Service holds the rank of Commodore.
 Marine troops
During the era of the Roman empire, the naval forces included legionaries for boarding actions. These were troops primarily trained in land warfare, and did not need to be skilled at handling a ship. Much later during the age of sail, a component of marines served a similar role, being ship-borne soldiers who were used either during boarding actions, as sharp-shooters, or in raids along the shore.
The Spanish Infantería de Marina was formed in 1537, making it the oldest current marine corps in the world. The United States Marine Corps became a separate arm in the United States military, with their own equipment. However the U.S. Navy SEALs and the British Royal Marines now serve a similar function, being a ship-based force specially-trained in commando-style operations and tactics as part of the navy. The Royal Marines also have their own special forces, the SBS (Special Boat Service); similar to the US Navy SEALs and the Boat Troops of the SAS.
"Navy" came via Old French from Latin navigium = "fleet of ships" from navis = "ship" and agere = "to drive" (as in driving a herd of animals) or "to get something done".
"Naval" came from Latin navalis = "pertaining to ship" (which it means in the biological name Teredo navalis), but due to resemblance became changed to "pertaining to navy".