 A superior force of Nationalist troops captured Yan'an in March 1947, but Zhou's intelligence agents (primarily Xiong Xianghui) were able to provide Yan'an's commanding general, Peng Dehuai, with details of the KMT army's troop strength, distribution, positions, air cover, and dates of deployment.This intelligence allowed Communist forces to avoid major battles and to engage Nationalist forces in a protracted campaign of guerrilla warfare that eventually led to Peng achieving a series of major victories.By February 1948 over half the KMT troops in the northwest were either defeated or exhausted.