On July 6, 1938 the Japanese Kwantung Army decoded a message sent by the Russian commander in the Posyet region to Soviet headquarters in Khabarovsk. The message recommended that Russian soldiers be allowed to secure unoccupied high ground west of Lake Khasan, most notably the disputed Changkufeng Heights, because it would be advantageous for the Soviets to occupy terrain which overlooked the Korean port-city of Rajin, as well as strategic railways linking Korea to Manchuria. In the next two weeks, small groups of Soviet border troops moved into the area and began fortifying the mountain with emplacements, observation trenches, entanglements and communication facilities. On Jul 31, Sato's regiment launched a night sortie on the fortified hill. In the Changkufeng sector, 1,114 Japanese engaged a Soviet garrison of 300, eliminating them and knocking out 10 tanks. On 31 July, People's Commissar for Defence Kliment Voroshilov ordered combat readiness for 1st Coastal Army and the Pacific Fleet. The Soviets gathered 354 tanks and assault guns at Lake Khasan, including 257 T-26 tanks (with 10 KhT-26 flame-throwing tanks), 3 ST-26 bridge-laying tanks, 81 BT-7 light tanks and 13 SU-5-2 self-propelled guns. The chief of the Far East Front, Vasily Blücher, arrived at the front line on August 2, 1938. Under his command, additional forces were moved up and from August 2–9, the Japanese forces at Changkufeng were attacked. Such was the disparity of forces that one Japanese artillery commander observed that the Soviets fired more shells in one day than the Japanese did in the two-week affair. Despite this, the Japanese defenders organized an anti-tank defense, with disastrous results for the poorly coordinated Soviets, whose attacks were defeated with many casualties. Thousands of Soviet troops were killed or wounded and at least 46 tanks were knocked out, with another 39 damaged to varying degrees.
