units marked the dawn of a new branch of armed forces, which would be called armored forces. In 1937, the Central Directorate of Mechanisation and Motorisation was renamed to Directorate of Automated Armored Units (Автобронетанковое управление) and then to Chief Directorate of Automated Armored Units (Главное автобронетанковое управление, Габту, GABTU). Soviet armored units gained some combat experience during the Battle of Lake Khasan (1938), Battle of Khalkhin Gol (1939) and Winter War with Finland (1939–1940). In August 1938, the four mechanised corps were converted into tank corps. Each was authorized 12,710 men, between 560 and 600 tanks, and 118 artillery pieces. The corps included two light tank brigades (equipped with BT and T-26 tanks), a motor rifle and machine gun brigade, and a communications battalion. The 5th Mechanized Corps became the 15th Tank Corps, the 7th Mechanized Corps became the 10th Tank Corps, the 11th Mechanized Corps became the 20th Tank Corps, and the 45th Mechanized Corps became the 25th Tank Corps. In the summer of 1939, all three brigades of the 20th Tank Corps were detached from the corps and sent into combat during the Battles of Khalkhin Gol. The 15th and 25th Tank Corps fought in the Soviet invasion of Poland in September 1939. As a result of the Soviet assessment of the tank corps as being unwieldy and difficult to control, shown by repeated traffic jams caused by the tank corps in Poland, the Main Military Council ordered their disbandment on 21 November, replacing the tank corps with 15 motorized divisions, each with two motorized rifle regiments, an artillery regiment, and a tank regiment. The tank corps were not actually disbanded until January 1940, by which time the 10th Tank Corps had seen brief service in the Winter War in December 1939. Besides the operational armoured and mechanised formations, separate tank battalions within rifle divisions existed. These were meant to reinforce rifle units for the purpose of breaching enemy defenses. They had to act in cooperation with the infantry without breaking away from it and were called tanks for immediate infantry support (танки непосредственной поддержки пехоты). With the fall of France, the People's Commissariat for Defense authorized formation of new mechanized corps. Unlike the corps formed in the 30's (which consisted of brigades), these corps (with over 1000 tanks each on paper) would consist of two tank and one mechanized division plus support units (Red Army Handbook