In 1936, Hu joined an expeditionary force led by Zhang Guotao. The objective of Zhang's 21,800+ strong force, was to cross the Yellow River, to expand the communist base west of Shaanxi, and to link up with forces from the Soviet Union or with the Xinjiang warlord Sheng Shicai, who was an ally of the communists and the Soviet Union. Zhang Guotao's forces were soundly defeated by the local Nationalist warlords, the Ma clique. Hu Yaobang, along with Qin Jiwei, became two of the thousands of prisoners-of-war captured by Ma clique's forces. Hu was one of only 1,500 prisoners-of-war whom Ma Bufang decided to use as forced labor rather than execute.