BT tanks saw service in the Second Sino-Japanese War, Spanish Civil War, Battle of Khalkhin Gol (Nomonhan), the Winter War in Finland, the Polish campaign, and in the entire World War II.
They first saw action in the Spanish Civil War. A battalion of BT-5s fought on the Republican side, and their 45 mm guns could easily knock out the opposing German and Italian light tanks. The Chinese Nationalist Army also had 4 BT-5s and they fought against the Japanese Imperial Army during the Second Sino-Japanese War.
World War II in East-Asia
World War II was firstly broken in East-Asia, 7th July, 1937.During the Battles of Khalkhin Gol (also known as the Nomonhan Incident), which lasted from May to September in 1939, BT tanks were easily attacked by Japanese "close quarter" teams (tank killer squads) which were - in lieu of anti-tank weapons - armed with petrol bottles (later called "Molotov cocktails"). The Soviet BT-5 and BT-7 light tanks, which had been operating in temperatures greater than 100F on the Mongolian plains, easily caught fire when a Molotov cocktail ignited their gasoline engines. General Georgy Zhukov made it one of his "points" when briefing Joseph Stalin, that his "...BT tanks were a bit fireprone...." Conversely, many Japanese tank crews held the Soviet 45mm anti-tank/tank guns in high esteem, noting, "...no sooner did they see the flash from a Russian gun, than they'd notice a hole in their tank, adding that the Soviet gunners were accurate too!"
After the Khalkhin Gol War in 1939, the Soviet military had broken into two camps; one side was represented by Spanish Civil War veterans General P. V. Rychagov of the Soviet Air Force, Soviet armour expert General Dimitry Pavlov, and Stalin's favorite, Marshal Grigory Kulik, Chief of Artillery Administration. The other side consisted of the Khalkhin Gol veterans led by Generals Zhukov and G.P. Kravchenko of the Soviet Air Force. Under this cloud of division, the lessons of Russia's "first real war on a massive scale using tanks, artillery, and airplanes" at Nomonhan (Khalkhin Gol) went unheeded. Consequently, during the Finland War (Winter War) the BT-2 and BT-5 tanks were less successful.
During the final weeks of World War II, a significant number of BT-7 tanks took part in the invasion of Japanese-occupied Manchuria, in August 1945. This was the last combat action for the BT tanks.
World War II in Europe
During the Second World War in Europe, BT-5 and BT-7 tanks were used in the 1939 Soviet invasion of Poland, and in large numbers in the battles of 1941 - during which thousands were abandoned or destroyed. A few remained in use in 1942, but were rare after that time. The Red Army planned to replace the BT tank series with the T-34, and had just begun doing so when the German invasion (Operation Barbarossa) took place.