Stole this from another forum.
Prelude
The incident began on 11 May 1939, when a Mongolian cavalry unit of some 70-90 men entered the disputed area in search of grazing for their horses, and encountered Manchukuoan cavalry who drove them out of the disputed territory. Two days later the Mongolian force returned and the Manchukoans were unable to evict them.
At this point the Japanese Guandong Army became involved -- a reconnaissance unit under Lt. Col. Yaozo Azuma was sent to engage the Mongolians on 14 May, but they retreated west of the river with few losses. Joseph Stalin ordered STAVKA, the Red Army's high command, to develop a plan for a counterstrike against the Japanese. To lead the attack, Georgy Zhukov, a young officer of promise, was chosen.
The Mongolians and Soviets continued to build up forces in the area, and Azuma's force returned a week later. This time the Japanese forces were surrounded by superior numbers of Soviet and Mongolian infantry and tanks, and on 28-29 May the Azuma force was destroyed, suffering 8 officers and 97 men killed and one officer and 33 men wounded, with 63% casualties. The Guangdong Army decided that the area was not worth the expenditure of any more Japanese blood.
Throughout June, however, there were continuing reports of Soviet and Mongolian activity on both sides of the river near Nomonhan, and small-scale attacks on isolated Manchukoan units. At the end of the month the local Guandong Army commander, Lt. Gen. Michitaro Komatsubara, was given permission to "expel the invaders". The Japanese operation started on 1 July and was initially successful in crossing the Halha river. However, by the evening of 3 July the attack stalled and the Soviet forces, led by Zhukov, threw the Japanese back over the river. The front then stabilized with only minor actions for the summer.
The Battle
Finally, in mid-August, Zhukov decided it was time to break the stalemate. He deployed approximately 50,000 Russian and Mongolian troops of the 57th Special Corps to defend the east bank of the Halhin Gol River, then crossed the river on 20 August to attack the elite Japanese with three infantry divisions (70,000 men in all), massed artillery, a tank brigade, and the best planes of the Red Air Force.
Japanese doctrine at the time was for front-line troops to hold their positions with high rates of fire, and await relief actions from the rear. While very successful against the lightly armed Chinese forces, the Soviet tanks turned the tables on them entirely, and the front lines were cut off. Two complete divisions were surrounded while the other forces were scattered. On 27 August the Japanese attempted to break out of the encirclement, but failed. When the surrounded forces refused to surrender, Zhukov wiped them out with artillery and air attacks. The battle ended 31 August with the complete destruction of the Japanese forces.
Aftermath
Following the battle, the Red Army attacked what remained of the Japanese forces and drove them back into Manchukuo. On 16 September the Japanese asked for a cease-fire and nearly two years later signed a treaty in which they agreed to abide by the existing border.
Of the 30,000 troops on the Japanese side, 8440 were killed and 8766 wounded. The Red Army committed 57,000 infantry, 498 tanks, and 346 armoured cars to the battle, and claimed total losses (killed and wounded) of 9284 men. After the collapse of the Soviet Union in 1991, new documents about the battle changed the numbers considerably. The actual number of losses in the battle was 23,926, of whom 6,831 killed, 1,143 reported missing and 15,952 wounded. While the Red Army did win the battle, it was not a one-sided battle as previously believed.
