Other commentators can address land warfare, but I will point out that for much of the 16th century, the Ottomans were considered invincible at sea. They owed this in part to a remarkable run of dynamic naval commanders, including Hayreddin Barbarossa, Dragut, and Uluj Ali, who rose from common cutthroats at sea to powerful warlords with imperial titles. Beyond them, though, the Ottomans were consistently successive at seaborne warfare. At the beginning of the 16th century, the Turks and the Spanish had consolidated control over opposite ends of the Mediterranean; their rivalry swallowed up the previously isolated struggles on the sea, and more or less defined the battle for supremacy on the Mediterranean.

Warfare on the Mediterranean was profoundly shaped by the capabilities and limitations of the primary instrument, the oared galley. Equipped and manned in different styles in many nations, it was a very versatile warship, able to function in pitched battle, amphibious landings and assault, commerce and coastal raiding, and sieges. However, the many hands needed to operate one and the limited space for storing provisions limited the strategic range of the galley; a prolonged blockade of a state's whole coastline was generally not practicable. They also needed precious skilled manpower and sophisticated support systems to be functional.

Seaborne warfare on the Mediterranean thus revolved around the capture and defense of fortified ports, which were used as bases for small scale raiding as part of a strategy of economic attrition. Making battle with the intention of destroying the enemy fleet and imposing a strangling blockade on the enemies' whole economy was not a prominent feature in this way of war. While small scale clashes between squadrons were often brutally one-sided, fleet engagements tended towards indecision, as the enemy on the defensive could back their ships against the shore, guns facing the sea; this is equivalent to a land army staying in its fortified camp. An admiral would thus only accept battle on the sea if he had a good chance of winning, which would pressure the enemy not to offer battle in the first place. Thus the main way to damage the enemy was by capturing trade vessels or raiding seaside towns and villages, inflicting economic damage; a slave in Algiers paid the king no taxes, and neither did a village of cinders. The galley fleets necessary to protect the coats represented an economic drain in their own right, and throughout the 16th century, Spain was plagued by debt and bankruptcy as its strategic commitments around the world multiplied.

Hayreddin Barbarossa, who struck out as a corsair with his brother Oruch, was the first of the great Barbary warlords, who rose from a simple sailor to ruler of Algiers after his brother died. Building a galley fleet of their own, they allied with the Ottomans, becoming governors of the new province of Algiers in exchange for aid against the Spanish. He was highly successful raiding Spanish possessions in the Mediterranean; it was said he robbed the King of Spain of 70,000 subjects by helping Spanish Muslims escape to North Africa, and repeatedly outmaneuvered Spanish squadrons. He assaulted Tripoli, which had become the base of the Knights of St. John after they had been driven from Rhodes; he stormed the Peñón, the Spanish island fortress commanding the harbor of Algiers, then captured wholesale the relief squadron. He became a boogeyman in the Mediterranean, the bane of Christians and 'The King of Evil.'

When the Genoese admiral Andrea Doria savaged the Greek coast with impunity, Suleiman made Barbarossa his grand admiral in a lavish ceremony in Constantinople, putting him at the head of a powerful fleet to give Spain his reply. He evaded the watchtowers on the Adriatic coast of Italy and raided the Tyrrhenian coast with terrifying skill, burning towns, enslaving people, and smashing warships caught unprotected; people fled Rome itself at the word of his approach. With 80 ships, Barbarossa conquered Tunis, which had been a Spanish vassal; he was rumored to be killed in the 1535 Spanish counteroffensive, but returned all too alive to devastate the Spanish coast again.

A few years later, he aided in capturing several Illyrian islands under Venetian control and though he did not capture the fortress, he laid waste to much of Corfu. These campaigns seriously eroded the manpower base of the republic; Venice relied heavily on the Dalmatian islands for their oarsmen and marines. This prompted the Venetians to call for a Holy League to lead a counteroffensive against the Ottomans. Under Andrea Doria, the Holy League sought out Barbarossa's fleet, which sheltered itself in the gulf of Preveza; this place had witnessed the Battle of Actium fifteen hundred years before.

Barbarossa had chosen his position at Preveza carefully; the narrow entrance of the gulf and the fortifications commanding the strait made it impossible to assault directly, and his proximity to a friendly shore ensured enough supplies for his fleet to stay there as long as he liked. Doria, on the other hand, knew his supplies were running low, and unable to capture the fortress of Preveza, knew there was nothing for him to do. However, when he attempted to retreat in the night, morning found his swift galleys had outpaced the sailing ships that accompanied the fleet. Barbarossa seized the opportunity, sailing out of the gulf to overwhelm and gobble up the stranded roundships; Dragut led the way with a squadron of light galleys. Barbarossa did not losing a single ship in the battle, and sunk or captured 48. While not a mortal blow in its own right, the ignominious failure split Venice from Spain; they would not ally again for 32 years.

Barbarossa continued the war with Spain, leading a powerful fleet up the coast of Italy, where he wintered in the harbor of Toulon; the alliance of France and the Ottomans scandalized Europe, but it was strategically devastating. The following campaign season, his fleet rampaged down the Tyrrhenian coast again, sacking substantial towns and taking more than six thousand people into slavery. The Spanish fleet was too dispersed to coordinate an effective response; assembling an armada took time, and corsairs like Barbarossa had wrested the strategic initiative from the Spanish.

The Ottoman way of war at sea was about gathering overwhelming force to strike a precise point while the enemy was helpless to respond, whether it meant laying waste to helpless towns or capturing key fortresses. Even in the lull between blows, the corsairs spread terror everywhere the sea could be heard; people simply vanished, either to a life in chains or to be held for ransom. Success wasn't measured in ships sunk, but in captives taken, or in the price of insurance on trading vessels. On the strategic defensive, the Spanish had to keep their galleys manned year-round, which resulted in astronomical upkeep costs as the galleys burned men like fuel, while the Ottomans could build up and demobilize as needed.

While Barbarossa died a couple years after his terrifying cruise down the Italian coast, his successor, Dragut, was no less terrifying. Dragut had served as a corsair captain under Barbarossa for many years, leading a squadron of galiots in many campaigns, and now took over the piratical principality that was Algiers. For a time, he used the bay of Djerba in what is today Libya as his base. When confronted by a superior galley force under Doria and trapped in the bay, he was able to escape by hauling his ships over land and down the creeks on the other side of the island, escaping to pillage Malta and expel the Knights of St. John from their base at Tripoli. When the island of Gozo refused to give him the body of his brother, he sold the entire population of the island into slavery.

He proved so successful in raiding Spanish possessions in the Western Mediterranean that they mustered a major expedition to drive him from his bases in Djerba and Tripoli. The Ottomans responded decisively, dispatching a powerful fleet under Piali Pasha, who caught the Spanish allied fleet in the act of reembarking; seeing their disorder, his galleys raised their sails to close as quickly as possible. This was a risky move, as damage to a ship's mast could cause it to fall, crushing dozens of men chained in place or other wise packed together. However, galleys were highly vulnerable to flanking; their marines and firepower was all concentrated at the bow, and being able to fire a close range artillery volley while the enemy could not respond was an immense advantage for the attacker. Moreover, Turkish galleys were known to be swifter and more maneuverable, giving them an advantage in this kind of disordered melee. Piali's calculations were proven correct, and the battle only lasted a few hours.

Ottoman losses were trifling, while the Spanish lost near-irreplacable skilled manpower, with at least 600 experienced mariners and 2500 sailor-gunners killed. Whereas the Atlantic tradition of naval warfare stresses ships, manpower was the key to seaborne warfare on the Mediterranean; commanders would gladly sacrifice their vessels if it meant the men would live; ship hulls were cheap, costing only a third of what a year of crew pay and provision did. War at sea in the 16th century was not carried out by men who learned their skills through training by the armed forces, the way it is today; rather, states relied on recruiting people who had learned their trade through a lifetime of experience. If a galley fleet was not well handled, a large battle could send a whole generation of men with a lifetime of maritime experience to a watery grave. The Spanish garrison left on the island was besieged and wiped out; the Ottomans left behind a mound of skulls that remained in place until the 19th century.