Navy
Etymology and meanings: First attested in English in the early 14th century, the word "navy" came via Old French navie, "fleet of ships", from the Latin navigium, "a vessel, a ship, bark, boat", from navis, "ship". The word "naval" came from Latin navalis, "pertaining to ship"; cf. Greek ναῦς (naus), "ship", ναύτης (nautes), "seaman, sailor". The earliest attested form of the word is in the Mycenaean Greek compound word 𐀙𐀄𐀈𐀗, na-u-do-mo (*naudomoi), "shipbuilders", written in Linear B syllabic script.
The word formerly denoted fleets of both commercial and military nature. In modern usage "navy" used alone always denotes a military fleet, although the term "merchant navy" for a commercial fleet still incorporates the non-military word sense. This overlap in word senses between commercial and military fleets grew out of the inherently dual-use nature of fleets; centuries ago, nationality was a trait that unified a fleet across both civilian and military uses. Although nationality of commercial vessels has little importance in peacetime trade other than for tax avoidance, it can have greater meaning during wartime, when supply chains become matters of patriotic attack and defense, and when in some cases private vessels are even temporarily converted to military vessels. The latter was especially important, and common, before 20th-century military technology existed, when merely adding artillery and naval infantry to any sailing vessel could render it fully as martial as any military-owned vessel. Such privateering has been rendered obsolete in blue-water strategy since modern missile and aircraft systems grew to leapfrog over artillery and infantry in many respects; but privateering nevertheless remains potentially relevant in littoral warfare of a limited and asymmetric nature.

History: Naval warfare developed when humans first fought from water-borne vessels. Before the introduction of the cannon and ships with enough capacity to carry them, 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 vessel so its occupants could be attacked hand-to-hand. Naval warfare continued in this vein through the Middle Ages until the cannon became commonplace and capable of being reloaded quickly enough to be reused in the same battle. 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 Chola Dynasty in Southern India had a navy composed of trade ships transporting  armies overseas. The Chola Navy reached its peak under Rajendra I, and was most notably used in invasions of Sri Lanka and Southeast Asia.
Nusantaran thalassocracies made extensive use of naval power and technologies. This enabled the seafaring local people (either Malays of Srivijaya or Javanese of Mataram) to attack as far as the coast of Tanzania and Mozambique with 1000 boats and attempted to take the citadel of Qanbaloh, about 7,000 km to their West, in 945–946 AD.: 110 : 39  In 1350 AD Majapahit launched its largest military expedition, the invasion of Pasai, with 400 large jong and innumerable smaller vessels. The second largest military expedition, invasion of Singapura in 1398, Majapahit deployed 300 jong with no less than 200,000 men. The average jong used by Majapahit would be about 76.18–79.81 m LOA, carrying 600–700 men, with 1200–1400 tons deadweight.: 60–62 

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 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. 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. As a response to growing naval influence of the navies of Portuguese, the warrior king of the Marathas, Shivaji laid the foundation of the Maratha navy in 1654.
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 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 CSS Virginia and USS Monitor during the American Civil War (1861–1865) is often cited as the beginning of this age of maritime conflict. The Russian Navy was considered the third strongest in the world on the eve of the Russo-Japanese War, which turned to be a catastrophe for the Russian military in general and the Russian Navy in particular. Although neither party lacked courage, the Russians were defeated by the Japanese in the Battle of Port Arthur, which was the first time in warfare that mines were used for offensive purposes. The warships of the Baltic Fleet sent to the Far East were lost in the Battle of Tsushima. A further step change in naval firepower occurred when the United Kingdom launched HMS Dreadnought in 1906, 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, Nazi Germany's submarine fleet of U-boats almost starved the United Kingdom into submission and inflicted tremendous losses on U.S. coastal shipping. The German battleship Tirpitz, a sister ship of 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 at 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. In the late 20th and early 21st centuries, the United States Navy possessed over 70% of the world's total numbers and total tonnage of naval vessels of 1,000 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.