 On the night of July 7, 1937, Chinese and Japanese troops exchanged fire in the vicinity of the Marco Polo (or Lugou) Bridge, a crucial access-route to Beiping.What began as confused, sporadic skirmishing soon escalated into a full-scale battle in which Beiping and its port city of Tianjin fell to Japanese forces (July–August 1937).On July 29, some 5,000 troops of the 1st and 2nd Corps of the East Hopei Army mutinied, turning against the Japanese garrison.