Seventy years ago, a massive border clash in Outer Mongolia between the forces of the Soviet Union and the Imperial Japanese Army sent shock waves across the world, which eventually decided the course and outcome of World War II. From May to September 1939, Japan and the Soviet Union fought a fierce, large-scale undeclared war on the Mongolian Steppe that ended with a decisive Soviet victory. The outcome of that conflict was that Japan reoriented its strategic emphasis toward the south, leading to war with the United States, Britain, and the Netherlands. As a result of the Japanese defeat, the Soviet Union was able to free itself from the fear of fighting on two fronts, thus vitally affecting the course of the war with Germany. In Japan this undeclared war was known as the Nomonhan Incident, while in the Soviet Union it was known as “The Battle of Khalkhin Gol.”
    After the occupation of Korea in 1905, and Manchuria in 1931, Japan turned its military interest toward Soviet territories. In 1939, Manchuria was a puppet state known as Manchukuo, The Japanese insisted that the border between Manchukuo and the Mongolian People's Republic was the "Khalkha River" (Khalkhin Gol). In contrast, the Mongolians and their Soviet allies maintained that the border ran some 10 miles east of the river, just east of Nomonhan village. The principal occupying army in Manchukuo was the Kwantung Army. This Army consisted of some of the best Japanese units in 1939. However, the western region of Manchukuo was garrisoned by the newly formed 23rd division of the Imperial Japanese Army at Hailar under Lt. General Michiataro Komatsubara and included several Manchukuoan army and border guard units.
    During this period, the relationship between the Kwantung Army and the Imperial Japanese Army's General Staff could be described at best as rivalry. Normally in a modern society the military is subject to a strict chain of command. The Japanese army in the 1930s was different in that important policy decisions were often made at relatively low levels, by people on the spot. Then the Army General Staff and the government in Tokyo would have to go along, if only out of fear of angering nationalist sentiment within the military. In practice, the Kwantung Army operated more like an independent entity as in the days when Japan was a warring feudal state. The Japanese leadership was cautious enough to not order aggressive acts itself, but it also was afraid to discipline the ultra-nationalist militarists within the army. In other words, it was the lack of a strong leader in Japan that dictated the course of events.
    The incident began on 11 May 1939. A Mongolian cavalry unit of some 70-90 men had entered the disputed area in search of grazing for their horses. On that day, Manchukuoan cavalry attacked the Mongolians and drove them back across the Khalkhin Gol. On 13 May, the Mongolian force returned in greater numbers and the Manchukoans were unable to dislodge them.
    On the 14th, Lt. Col. Yaozo Azuma led the reconnaissance regiment of the Japanese 23rd Division, supported by the 64th Regiment of the same division, under Colonel Takemitsu Yamagata, into the disputed territory and the Mongolians withdrew. However, Soviet and Mongolian troops returned to the disputed region and Azuma's force again moved to evict them. This time things turned out differently, as the Soviet-Mongolian forces surrounded Azuma's force on 28 May and destroyed it. The Azuma force suffered eight officers and 97 men killed and one officer and 33 men wounded. Acting against direct orders from Tokyo, the Kwantung Army unilaterally decided to retaliate sending the 23rd Infantry Division two tank regiments plus significant artillery and air support to settle the issue.
    In preparation for the main Japanese thrust toward the Khalkha River, the Japanese Army Air Force launched an air attack on 27 June. The Japanese 2nd Air Brigade struck the Soviet air base at Tamsak-Bulak in Mongolia. It is very hard to sort out losses in the air war, as both sides minimized their losses and exaggerated their victories. However, the Japanese surprised the Soviets with their sudden strike. The Nakajima Ki-27, the Japanese Army Air Force's new, all-metal monoplane fighter, was clearly superior to the Soviet Poliparkov I-15s, I-16s, and somewhat better than I-153 fighters. The Japanese pilots were better trained as well. On the whole, the Japanese won this engagement, destroying half again as many Soviet planes as they lost, but the strike had been ordered by the Kwantung Army without getting permission from Imperial Japanese Army headquarters in Tokyo. Tokyo promptly ordered the Japanese Army Air Force not to conduct any more air strikes.
    Phase two of the offensive began in early July with the 23rd Division crossing the upper reaches of the Khalkha River while mechanized elements struck directly at Soviet forces on the right bank of the river. After making some initial gains the Japanese attack stalled. When the Soviets counterattacked, the Japanese found their lightly armored and under-gunned tanks hopelessly outclassed by Soviet BT-5/7 models. The Japanese rushed additional infantry, armor, aircraft and heavy artillery to the front, renewing the offensive in late July. Stopped cold in the face of fierce Soviet resistance, the Japanese now dug in and waited.
    In Moscow, Josef Stalin and his foreign minister, Vyachaeslav Molotov, observing the Japanese’ aggressive move in Outer Mongolia, began to worry about the possibility of fighting a two front war in the future. With events in Europe rapidly unfolding, Josef Stalin and the Soviet High Command decided that Japan must be stopped. The outcome of any move against the Japanese forces in Asia must be decisive, and a clear lesson should also be driven into the Japanese Army General Staff heads that fighting the Soviet Union is a losing proposition.
    In early June, Stalin sent to the scene an aggressive new commander with “carte blanche.” He was Lt. Gen. Georgi K. Zhukov, age 42. On July 1st the 1st Front Army was organized under his command. As soon as he learned of the Japanese penetration, he launched a coordinated three-pronged counterattack by the 11th Tank Brigade, and a motorized infantry regiment and a brigade of armored cars. The Japanese themselves launched a counter attack to try to hold onto their gains, but the Japanese antitank weapons were not adequate against Soviet armor. The Japanese, in desperation, resorted to suicide attacks with squads of men hurling satchel charges and Molotov cocktails, but they could not stop the Soviet onslaught. In two days of heavy fighting the Soviets retook the Baintsagan Heights and threatened the one pontoon bridge the Japanese had across the Khalkha River, forcing the Japanese to withdraw over the river.
    All through early and mid August Zhukov quietly moved up reinforcements. The troops moved only at night, masking the sound of tanks massing with late night bombing raids and small arms fire on Japanese positions. Zhukov deliberately ordered his men to continue constructing defensive positions to lull Japanese suspicions, while sending out patrols to scout enemy positions by night. Zhukov, absorbing the tactical lessons of the Spanish Civil War, insisted on careful cooperation between the air and ground forces. Air reconnaissance was used to pinpoint Japanese defensive positions, and pilots were made to participate in ground briefings with the Red Army. By mid August Zhukov had five divisions and four armored brigades in position against just over two Japanese divisions.
    At 6:00 A.M., on August 20th, Zhukov struck. More than 50,000 Soviet and Mongolian troops moved forward along a 48-mile front, supported by 500 tanks, 346 armored cars, and 216 artillery pieces. Surprise was total. Soviet artillery outgunned the Japanese batteries, which were short on ammunition. Soviet bombardments cut phone lines, isolated Japanese units, and blasted apart flimsy dugouts. 200 SB-2 bombers, heavily supported by fighters, struck Japanese defenses and lines of communications. The Soviet bombers could fly at 20,000 feet, too high for the Japanese fighter planes. Soviet air losses were high, but they were able to achieve local air superiority over the battlefield from the Japanese.
    On August 26th a Japanese counterattack to relieve the trapped 23rd Division was halted by a Soviet tank brigade. The next day, the Japanese 23rd Division made a last-ditch effort to break out to the east. They were defeated. By August 31, 1939 the Japanese had been driven back out of the disputed territory. Of the 60,000 Japanese troops committed, some historians claim nearly 45,000 became casualties. The Imperial Japanese Army 23rd Infantry Division took 73 percent casualties. The 71st Regiment suffered more than 93 percent losses. In a painful lesson, the Japanese Army realized that the Soviet Army of 1939 with its new organization, leadership, equipment, and fire power, was very different from the Tsarist Army of 1905.
    The Kwantung Army had taken a savage beating. The Soviets took some 3,000 Japanese prisoners, many badly wounded. The Soviets were eager to indoctrinate them to Communism. Some 1,000 stayed on in the Soviet Union rather than face dishonor at home. Soviet casualties were also high. They admitted to a little over 9,000 casualties, but the actual total was closer to 17,000 or higher. But these were losses the Red Army could afford.
    At this point the Soviets could have pushed into Manchuria, but instead they halted at the line the Mongolian People’s Republic had claimed at the start of the conflict and dug in. All through this period the Soviet KGB had a spy ring operating in Tokyo under the masterful leadership of Richard Sorge. Sorge's information showed that the Japanese wanted an end to the fighting as soon as possible. Knowing this, as early as August 22, the Soviets offered the Japanese Ambassador, Togo Shigenori, in Moscow a cease fire.
    On 23 August 1939, the Soviets signed a Non-Aggression Pact with Nazi Germany, agreeing to divide Poland. The last hope of the 'Strike North' faction in the Japanese high command was dead. On September 15th, as German tanks closed in on Warsaw, Ambassador Togo signed a cease fire with the Soviets, to take effect on the 16th. Both sides agreed to exchange POWs and establish a joint commission to resolve disputes along the length of the border. As the Second World War engulfed Europe, Stalin was free to focus his attention in the West against Hitler.
    In Japan, the Kwantung Army and the Imperial Japanese Army in general, suffered a significant loss of influence. Lt. Gen. Michitaro Komatsubara, commander of the 23rd Infantry Division, was disgraced. In early September Lt. Gen. Kenkichi Ueda, commander of the Kwantung Army, was reassigned to Japan, effectively ending his career. The Kwantung Army ceased to be a law unto itself and was brought back under centralized control from Tokyo. The Japanese were very careful not to provoke the Soviets again. Even when they signed the Tripartite Pact with Germany and Italy in March of 1941, the Japanese hastened to sign a non-aggression pact with the USSR as well.
    In the end, Nomonhan ruined the so-called 'Strike North' faction that had dominated Japanese strategic thinking until then. Now the 'Strike South' faction, led by the navy, would dominate Japanese strategic thinking. The Strike South leaders looked enviously at the oil rich Dutch East Indies (modern Indonesia), at strategic Malaya and Singapore, at Burma and Indochina, as the new war in Europe paralyzed the British and the French. The only thing stopping the Japanese now was the US Pacific Fleet, at its base at Pearl Harbor.