David Ryan is the U.S. Navy representative assigned to the joint U.S.-Japan nuclear submarine Seabat for its maiden voyage, tasked with observing operations and maintaining oversight of the classified military project. When Captain Kaieda seizes control of the submarine, renames it Yamato, and declares independence, Ryan attempts to intervene and detain Kaieda for mutiny. This effort fails as Kaieda's crew disregards Ryan's orders, resulting in his capture and status as a prisoner aboard the Yamato. Despite his prisoner designation, Ryan experiences unusual leniency in confinement, retaining freedom of movement throughout the submarine without physical restraints and permitted by Kaieda to navigate the vessel unsupervised. His presence aboard the Yamato embodies the direct U.S. military interests in the submarine project and positions him as a tangible symbol of the geopolitical tensions between the United States and Japan following Kaieda's actions. Ryan's role remains defined solely by his function as the U.S. liaison during the mutiny and his subsequent captivity.