The first government in history to issue paper money, the Song dynasty was the ruling dynasty in China between 960 and 1279. A culturally rich period for the arts, philosophy, and social life, the dynasty also bolstered naval strength and developed revolutionary new military technology—augmented by the use of gunpowder—to repel invaders. Nevertheless, the Song dynasty was conquered in 1279 by the Mongol ruler Kublai Khan. What nautical tool was invented during the era? Discuss