Japan was having conflicts with the USSR at the same time they were fighting Chinese troops. The years 1938 and 1939 were rife with border wars as Japan tried to increase its land holdings. Most of the fighting was near Manchuria. In late July 1938, the Japanese Kwantung Army attempted to invade the country owned by the Soviet Union in order to rearrange the lines of demarcation. Soviet soldiers had recently moved into the area in order to oversee the port city of Najin and gain access to the railways.

Battle of Lake Khasan

Following suspicions by the Japanese, the Koreans began a formal protest of the Soviet occupation. Three days of fighting ensued, and it seemed the Japanese were gaining ground. After the Soviets called in reinforcements, however, the Japanese were swiftly defeated and forced to retreat. This skirmish was named the Battle of Lake Khasan or the Changkufeng Incident. After the disastrous event, the Japanese Prime Minister asked for a peace treaty between the two countries on August 11.

May 11, 1939 was the beginning of disaster. Soviet-Mongolian cavalrymen had entered Manchukuo, which was fortified by Manchukuoan cavalry units. A fight to push them out ensued, but they kept returning in ever-greater numbers. In total, almost 100 men were killed, along with eight officers.

It was a serious fight now. Japanese forces gathered up to 30,000 troops – the Soviets did the same. Japanese troops had the advantage with fighter jets and air bombs, which attacked the Soviet-owned air base. The strike, however, wasn’t sanctioned by the official Imperial Japanese Army headquarters, so troops were ordered to stop the air attacks immediately. The day was still proclaimed a victory for Japan.

It wasn’t the end of the invasions by the Soviet-Mongolians, however. Small-scale battled occurred throughout the month of June until the Japanese had enough. An order was made to force out the Soviet-Mongolians permanently. The plan was to march across the Khalkhyn Gol River and oust the Soviets. Then, the Tank Corps would attack the enemies on the other side of the Khalkhyn Gol and meet up with the other Japanese regiments.

The plan seemed to work as they steadily pushed back the Soviet, but they weren’t anticipating the Soviet counterattack of 450 tanks and armored vehicles. Fighting continued for two weeks as each side alternately attacked and retreated. At the end of the fortnight, the Japanese had lost over 5,000 men. A stalemate was declared.

Troops were ready to fight again by August 20, 1939. Japanese forces were crushed by a massive conglomeration of Soviet fighter jets, tanks, and foot soldiers. Soviets knew they had won this fight, but the Japanese commander Komatsubara didn’t agree. He started to plan a counterattack, but it was thwarted by a cease-fire pact.