In Central China the Japanese 11th Army was to be subject to the concentrated attack of the 5th and 9th War Areas, and supporting attacks by 6th and 3rd War Area, while 3rd War Area with support from Shantung Kiangsu War area isolated 11th Army from help from 13th Army downstream by its offensive on the Yangtze and at Hangchow. 3rd War Area was to attack 116th Division positions along the south bank of the Yangtze River between Wuhu and Hukou with its main force, to cut communications and attack traffic along it with mines and artillery to prevent the Japanese 13th Army from giving aid to the 11th Army up river. Shantung Kiangsu War Area was to attack along the Tientsin-Pukou Railway on the north bank of the river in support. To do this, 23rd Army Group organized columns made from the 50th, 21st, 86th and 25th Corps with three divisions each and 18th Corps with two. The force was divided into a Right Flank Army, Central Army and Left Flank Army.
Question: What Army was prevented from helping the Japanese 11th Army?
Answer: Japanese 13th Army