By the start of December, Japan's Central China Area Army had swollen in strength to over 160,000 men, though only about 50,000 of these would ultimately participate in the fighting. The plan of attack against Nanking was a pincer movement which the Japanese called "encirclement and annihilation". The two prongs of the Central China Area Army's pincer were the Shanghai Expeditionary Army (SEA) advancing on Nanking from its eastern side and the 10th Army advancing from its southern side. To the north and west of Nanking lay the Yangtze River, but the Japanese planned to plug this possible escape route as well both by dispatching a squadron of ships up the river and by deploying two special detachments to circle around behind the city. The Kunisaki Detachment was to cross the Yangtze in the south with the ultimate aim of occupying Pukou on the river bank west of Nanking while the Yamada Detachment was to be sent on the far north route with the ultimate aim of taking Mufushan just north of Nanking.