At the beginning of the 20th century, Japan regarded the Soviet Union as its greatest potential adversary. In 1931, after the Japanese Kwantung Army invaded northeast China, it directly confronted the Soviet Army along the Sino-Soviet border. To strengthen preparations for war against the Soviet Union, the Kwantung Army began constructing fortifications. Starting in 1934, the Japanese built 17 fortresses, comprising more than 80,000 permanent structures, along a 5,000-kilometre stretch of the border. This defensive line ran from Hunchun in Jilin Province in the east, through Heilongjiang Province in the centre, and extended to Hailar and Arshan in Inner Mongolia in the west. To defend against the Soviet Far East Front, the Japanese concentrated their fortifications in the East Manchuria region, which accounted for more than half of the total number of fortresses. The largest and most well-known of these was the Hutou Fortress. Hutou Fortress, located in Hulin County, Heilongjiang Province, near Hutou Town, is positioned among the hills of the Wunda Mountains, with the Firestone Mountains to the west and the Ussuri River to the east. The fortress spans 12 kilometers at the front and extends 6 kilometers deep at the back. It consists of five key positions: Mangtu Mountain, Tiger North Mountain, Tiger East Mountain, Tiger West Mountain, and Tiger Tsunami Mountain. These positions were interconnected by pits and communication trenches. Due to its large scale, complex structure, and comprehensive facilities, the Kwantung Army boasted that it was the 'Oriental
Maginot Line'. Between 1934 and 1939, the Kwantung Army invested hundreds of millions of dollars in constructing the Hutou Fortress, employing hundreds of thousands of Chinese laborers and prisoners of war. These workers were transported to the fortress under harsh conditions, often described as "hell on earth." They were poorly clothed, underfed, and forced to work more than ten hours a day in physically demanding tasks. Countless workers died from exhaustion, illness, or were killed outright. In March 1939, the Kwantung Army established the 4th Border Guard Brigade and stationed it at Hutou Fortress. By 1941, the fortress reached its peak strength, with the garrison numbering around 12,000 soldiers, and the fortifications were heavily armed. However, after the outbreak of the Pacific War, the Japanese military shifted its strategic focus to the southern theater, drawing resources away from the Kwantung Army. As a result, the strength of the Kwantung Army in the region declined sharply, leading to a significant shortage of troops and equipment. By the time the Soviet Army launched its attack on Hutou Fortress, the Japanese garrison, the 15th Border Guard Brigade, had been reduced to only around 1,400 soldiers, with limited equipment and ammunition. ==Battle==