On September 18, 1931, hundreds of Japanese Kwantung Army fearfully launched an attack on the heavily defended North Camp of the Northeast Army. The Peking University battalion stationed at that time was the Seventh Brigade of the Feng Army, and the brigade commander was Zhang Xueliang's confidant and beloved general, Major General Wang Yizhe. At that time, there were more than 8,000 officers and men in the North Camp, well-equipped and well-trained; there were more than 100,000 Northeast Troops and more than 100,000 police officers and local militia regiments in the entire Northeast, and 200,000 elite Northeast Army troops in Guannei were in the hands of Zhang Xueliang, while the Japanese Kwantung Army's troops in the entire Korean Peninsula and Northeast China totaled only 20,000 or 30,000 troops.
It was under such a disparity in troop strength that when Rong Zhen, the chief of staff guarding fengjun's lair, asked Zhang Xueliang for instructions, Zhang Xueliang ordered the troops not to resist. Many people later said that this was an order issued by Chiang Kai-shek at that time, but in fact, it was not, in Zhang Xueliang's later years, there was a television station that did an interview with him, and Zhang Xueliang also admitted that it was his own order at that time, and had nothing to do with Chiang Kai-shek. Zhang Xueliang's move made 30 million fathers and elders in the northeast region become slaves in just three months, and the Japanese paid very small losses and easily occupied northeast China.
The day after the September 18 Incident, the Japanese rushed into the Shenyang Marshal's Mansion, when the Japanese were counting the Zhang family's property, they found that the Bank of Tianjin and HSBC had ten million, the Bank of Korea and the Zhenglong Bank had two million. Zhang Xueliang's private banks, money houses, ticket numbers, houses, and land in various parts of the northeast were also confiscated by the Japanese as reverse production. The Japanese army retrieved 80,000 gold bars from the Marshal's Mansion, a total of 2.56 million taels of gold, and transported them directly to the Japanese mainland.
More than half of China's heavy industry, especially its military industry, was in the northeast at that time. During Zhang Zuolin's lifetime, he appointed Yang Yuting as the superintendent, and at great expense, established the largest arsenal in the country at that time, the Fengtian Arsenal. At its peak, the Fengtian Arsenal had more than 8,000 machines and more than 30,000 workers. At the time of the September 18 Incident, the arsenal had 4,000 rifles, 400 light machine guns, more than 100 heavy machine guns, and 120 tons of TNT explosives, and the arsenal could also manufacture Japanese 37 mm flat-fire guns, Japanese 75 mm field guns, mountain guns, mortars, anti-aircraft guns, Japanese 105 mm cannons, Japanese 150 mm howitzers, gram 75 mm mountain guns, Austrian 77 mm field guns, and Austrian 100 mm howitzers.
After the September 18 Incident, the Japanese army captured 150,000 rifles, more than 3,000 light and heavy machine guns, thousands of artillery of various types, more than 200,000 shells, and countless bullets in Shenyang alone. The Shenyang Mortar Factory is also a large-scale arsenal, and the Japanese army has captured more than 2,500 mortars and more than 500,000 shells at the Shenyang Mortar Factory. The Northeast Army also had the largest arsenal in the country at that time, and all 265 aircraft of the Bong Army were captured by the Japanese Kwantung Army.
After 1931, the rich coal resources in the northeast, nickel ore, iron ore, gold ore, forestry, grain and other resources were developed and utilized by the Japanese, and a steady stream of them were transported back to Japan, so that the Japanese gradually developed the strength to invade China in an all-round way, which greatly alleviated Japan's economic crisis. Relying on the rich resources of the northeast, the Japanese Kwantung Army also developed from a mere 20,000 or 30,000 people to a million troops at the outbreak of the Pacific War, becoming the largest number, best equipped, and most effective unit among the four major Japanese fronts.