In the Spanish Civil War (1936–1939), a regiment of 50 BT-5s fought on the Republican side. They were manned by the members International Brigades trained in USSR and by some Soviet tankists. Their first combat on 13 October 1937 during the Zaragoza Offensive was disastrous: 13 tanks were lost due to bad tactics. Later, 12 more were lost from December 1937 to February 1938 during the Battle of Teruel. A few captured BT-5s were also used by the Nationalist side.