The T-26 first saw combat in the Spanish Civil War, where it showed its superiority over the current tanks of the period fielded by Italy and Germany. Then it saw combat against the Japanese in the Soviet-Japanese border conflicts at Lake Khasan and Khalkhin Gol, which exposed some of the design defects such as poor armour welding and the disadvantages of riveted constructions (the rivet would break off and could harm the crew inside). After that, the T-26 saw service in the Invasion of Poland and the Winter War against Finland. The Winter War effectively showed the Soviets that the T-26 was obsolete, as the 37 mm guns and anti-tank rifles and Finnish have could penetrate the light armour of the T-26. When World War II for Russia finally broke out in Operation Barbarossa, the T-26 proved inferior to the German's Panzer IIIs and Panzer IVs, plus the air supremacy of the Luftwaffe ensured many tanks were lost in the opening stages of Barbarossa.