In 1930 he became the commander of the 2nd Cavalry Brigade, giving seminars, held regular war-game exercises and large scale manoeuvres, and wrote manuals and textbooks on various military subjects. .
Zhukov's first victory was the Battle of Khalkan-Gol, fought in July and August, 1939, near Nomonhan, Mongolia, as part of the undeclared war with Japan. .
In April 1939 the 23rd Division of the Kwantung Army moved to its new target, Outer Mongolia; with orders to cross into Nomonhan, a deserted and disputed sector on the Manchukuo-Korean-Mongolian border. Japanese tanks, infantry and cavalry directed fierce attacks into this zone from May to July 1939, but were repulsed at all times by the defenders. Operations, on the Khalkan-Gol River, intensified rapidly. From May, Soviet bombers attacked into Manchukuo and Japanese bombers retaliated. The greatest air battles yet seen were taking place, with formations of 150-200 war planes deployed. Soviet anti-aircraft fire was highly effective and the Japanese air force barely held its own.
Concerned at a possible threat to the Trans-Siberian Railway occasioned by these expanded hostilities, the Soviet Defense Ministry dispatched to the sector its ablest commander, Lieutenant-General Georgi Zhukov, later a Marshal of the USSR and Stalin's most renowned commander in the German war. Zhukov arrived in June 1939. He arrived to find that the Kwantung Army had secured some vital high ground and quickly concluded his need for reinforcements. Before August 1939 he had acquired 550 front line aircraft, 500 state-of-the-art T34 tanks, twenty cavalry squadrons and thirty-five infantry battalions. He outnumbered the Kwantung Army three to two in infantry, by three squadrons in cavalry, and possessed a qualitative edge in armor. But above all, his army was to show a marked superiority in intelligence analysis, command, control and communication.
One of the first commanders to use radio signals intelligence to advantage, Zhukov sowed misinformation with the Japanese by broadcasting fictitious command orders, ciphered in codes he knew the Japanese could break.