MEDIEVAL WARFARE

Ships and Guns

Medieval European ships showed little if any improvement over their ancient Greek and Roman models. Borrowing from even earlier civilizations, the Greeks and Romans had perfected a basic type of ship for use on the Mediterranean Sea, something we call a galley.
Galley:  a relatively shallow draft vessel, which combined sail power with oars.  Such ships originally had a single mast, and on that mast, a single square sail.  Eventually, multiple masts were added.  The Greek trireme or "triple decker", with three decks for rowers, was developed during the Greek age of colonization.  This ship, which was essentially a military vessel, was one of the finest and fastest of all galleys, despite the fact that it predated by centuries the birth of Christ.
Problems confronting the galley:
(1)  The square sail catches a tail wind (a wind from behind) very efficiently and drives the ship forward at a good pace.  However, this same sail does not perform well when the wind is coming from the side or the front (bow) of the ship.  When this is the case, the ship makes a great deal of leeway (sideslip) and relatively little headway.  Consequently, Mediterranean galleys could only use their square sails effectively when they wanted to go in roughly the same direction as the wind.  Otherwise, they had to break out the oars and row.
(2)  Given the shallow draft of the galley, it was not very good in really rough seas.
Why did galley technology persist as long as it did?
In the ancient and medieval worlds, these failings were not critical.  The Mediterranean was a relatively calm sea, in which shallow-draft boats could function effectively.   It was also a relatively small body of water, where the use of oars was still feasible:  rowers would get you where you wanted to go or, at least, would get you to land, long before you ran out of food or your ships rotted or your crew died of scurvy.  Finally, the galley was well suited to coastal navigation.  And as late as the Middle Ages, mariners hugged the coastline as much as they could.  Consequently, until the end of the Middle Ages, the West did not improve much if any upon the Greek and Roman galleys that had sailed the Mediterranean a thousand years earlier.
In the Baltic and along the northern coasts of Europe, sailors got away from galleys with their shallow draft and numerous rowers.  But the ships which they developed were no better.  These northern ships tended to be ponderous hulks, which could be stuffed with cargo. However, since they were also dependent upon square sails, but lacked rowers, they were even less maneuverable than galleys.
Castles:   high sections near the bow and stern of medieval western ships which took their name because they looked like towers on a castle wall. The presence of such structures made ships more top-heavy than they would otherwisehave been.  Since these castles were used primarily to accommodate fighting men and guns, they were particularly pronounced on warships of the period. 
Viking Ship:  the West's one major advance in the art of shipbuilding before the end of the Middle Ages.  While still technically a galley, its hydrodynamic profile made it an improvement over those of the Mediterranean.  With such ships, the Norsemen had taken their long journeys, not only around the European continent, but far out into the North Atlantic (Iceland, Greenland, North America).  These early Viking voyages made little impression on the European consciousness.  Memory of their arrival in the New World was almost lost, except for the great epic poems, known as the sagas.  Nor did the Norse ships have much influence on the European art of shipbuilding.
Vinland:  an advanced base on the coast of North America established by the Vikings around the year 1000.  In the face of native resistance and inadequate support from back home, the Norse were soon forced to evacuate Vinland, though their contact with the New World apparently continued for several centuries.. In the struggle against European imperialism, the native peoples won the first round.
The galleys of the Mediterranean and the hulks of the north continued to dominate until the end of the Middle Ages.
During the Middle Ages, various cultures surpassed Europe in shipbuilding, among them the Chinese and the Arabs.  By the fourteenth century, both cultures were producing ships that were superior to anything in Western Europe. When the great Ming admiral, Cheng Ho, led Chinese fleets as far as the east coast of Africa early in the fifteenth century, some of his vessels were as large as, if not larger than, any other wooden ships ever built.  However, it was from the Islamic world that the west would lean about better ship-building techniques. In shipbuilding as in so many other things, Europeans had to turn to Islam for its models.
Advantages of Arab ships:
(1)  the shape of their hulls made them more hydrodynamic and sea-worthy.
(2)  Instead of square sails, the used what we call lateen sails.
Lateen Sail:  a triangular sail, with a spar running the length of its upper side to give it stability.  Its shape permit the ship using it to head up toward the wind, without anywhere near as much sideslip.
With their superior hulls and lateen rigging, Arab ships made the long voyages across the Indian Ocean to India and southeast Asia, voyages which gave them control over the eastern trade in oriental goods and spices.
The Role of Portugal:  In the west, the tiny kingdom of Portugal led the way toward European expansion.  For example, they adopted the lateen rig and hull shape pioneered by Moslem sailors and improved on the originals.
Caravel:  the ship developed by the Portuguese which had a deeper draft and used a lateen rigging.
Caravela redonda (literally the "squared caravel"):   later improvement on the simple caravel made by the Portuguese.  It combined the use of lateen and square sails on a single vessel which made for a combination of speed and  maneuverability .The squared caravel became the standard European vessel for long voyages, and the pattern for future evolution in shipbuilding.
The Development of Sea-going Firearms:  By the end of the 15th century, when the West came into conflict with other advanced societies, it had a pronounced lead in this field which it had built up toward the end of the Middle Ages.
Traditional forms of Naval Combat:
(1)  Ramming
(2)  Boarding
(3)  Firing missiles
Although ramming and boarding were the most common naval techniques in the ancient world, ships have carried artillery ever since the days of the Greeks and Romans. They would remain  the decisive factors in any sea battle until the end of the Middle Ages.
Pre-gunpowder forms of artillery:
(1)  catapults (for throwing stones)
(2)  ballistae (for shooting giant arrows)
(3)  Greek Fire:  one of the most advanced weapons developed during the Middle Ages, it was an incendiary liquid which would be pumped onto enemy ships and set afire.  Added to the arsenal by the Byzantine Empire (c. 700).
The introduction of gunpowder artillery changed this.
The gun was one of the major technological developments of the later Middle Ages/Renaissance.  Once it appeared on the scene, it was only a matter of time before some enterprising individual or government would place firearms aboard ship. This appears to have  first been done by ships of the city of Venice as early as the 1300s.
Originally, firearms tended to be grouped in the castles at the bow and stern and were primarily anti-personnel.  Their purpose was to sweep the enemy's deck of soldiers and sailors, not to sink his ship.  During the 15th century, this original role of naval gunnery began to change from simply "man-killing" to "ship-killing." 
Broadside:  the line of larger and heavier guns mounted along the side of the ship.  At first, these guns were located only along the upper deck.  Later, they were also placed on lower decks and fired through gunports.
Advantages of the broadside:
(1)  by getting the great weight of the guns down closer to the waterline, it increased the ship's stability.
(2)  it made it possible to get more and heavier guns on board.
Because of the broadside, and the improvement in the guns themselves, naval gunnery became ship-killing rather than just man-killing.
Tumbledown sides:  a slightly different hull shape which replaced the tapered side due largely to the introduction of broadside guns.  The new shape brought several advantages without much sacrifice in speed or maneuverability:
(1)  greater stability
(2)  more interior room
(3)  the fact that the open decks no longer came together boarding by an enemy much more difficult
By 1500, when the Portuguese began to fight the Arabs for control of Far Eastern trade, the new naval technology gave them an enormous advantage.  By then, the technology was fast spreading to other European nation soon to enter the colonial race (Spain, England, France, Holland).