daimyō clans undertook major naval building efforts in the 16th century, during the Sengoku period, when feudal rulers vying for supremacy built vast coastal navies of several hundred ships. The largest of these ships were called atakebune. Around that time, Japan seems to have developed one of the first ironclad warships in history, when Oda Nobunaga, a Japanese daimyō, had six iron-covered Ō-atakebune ("Great Atakebune") made in 1576 . These ships were called , literally "iron armored ships", and were armed with multiple cannons and large caliber rifles to defeat the large, but all wooden, vessels of the enemy. With these ships, Nobunaga defeated the Mōri clan navy at the mouth of the Kizu River, near Osaka in 1578, and began a successful naval blockade. The Ō-atakebune are regarded as floating fortresses rather than true warships, however, and were only used in coastal actions. European contacts The first Europeans reached Japan in 1543 on Chinese junks, and Portuguese ships started to arrive in Japan soon after. At that time, there was already trade exchanges between Portugal and Goa (since around 1515), consisting in 3 to 4 carracks leaving Lisbon with silver to purchase cotton and spices in India. Out of these, only one carrack went on to China in order to purchase silk, also in exchange for Portuguese silver. Accordingly, the cargo of the first Portuguese ships (usually about 4 smaller-sized ships every year) arriving in Japan almost entirely consisted of Chinese goods (silk, porcelain). The Japanese were very much looking forward to acquiring such goods, but had been prohibited from any contacts with by the Emperor of China, as a punishment for wakō pirate raids. The Portuguese (who were called Nanban, lit. Southern Barbarians) therefore found the opportunity to act as intermediaries in Asian trade. From the time of the acquisition of Macau in 1557, and their formal recognition as trade partners by the Chinese, the Portuguese started to regulate trade to Japan, by selling to the highest bidder the annual "captaincy" (ito wappu) to Japan, in effect conferring exclusive trading rights for a single carrack bound for Japan every year. The carracks were very large ships, usually between 1000 and 1500 tons, about double or triple the size of a large galleon or junk. That trade continued with few interruptions until 1638, when it was prohibited on the grounds that the priests and missionaries associated with the Portuguese