German encounter of Soviet T - 34 and KV tanks Prior to the invasion of the Soviet Union during World War II , the German armed forces were not aware of two newly developed Soviet tanks , the T - 34 and KV . As a result they were surprised when they met them in combat in June 1941 . The German ' s standard anti - tank weapons were found ineffective against these new Soviet tanks . This experience prompted a notable leap in tank development in Nazi Germany , mainly in an effort to counter these new threats . By June 22 , 1941 , the Red Army deployed almost 1 , 000 T - 34 and over 500 KV tanks , concentrating them into five of their twenty - nine mechanized corps . Initial encounters . At the beginning of Operation Barbarossa , Germany expected little more of the opponent ' s forces than the old T - 26 and BT tank s . While most of the Soviet Union ' s tank forces were composed of such tanks , they also surprised the enemy with two new notable designs ; the T - 34 and KV tank s . Both types were encountered very quickly , on the second day of the invasion – 23 June 1941 . The KV tanks were usually assigned to the same units as the more numerous T - 34 , and although they were much larger in size their overall performance was quite similar ; many sources discuss impact of both types together . The most used model of KV tank was the KV - 1 . It was in the Battle of Raseiniai where German forces encountered the Soviet KV tanks for the first time . The Soviet 2nd Tank Division from 3rd Mechanized Corps attacked and overran elements of the German 6th Panzer Division near Skaudvilė on 23 June . German Panzer 35 ( t ) light tanks and antitank weapons were practically ineffective against the Soviet armored giants — some of them were out of ammunition , but closed with and destroyed German antitank guns by literally driving over them . An account by the Thuringian 1st Panzer Division describes this battle . The next day , at a crossroads near Raseiniai , a single KV heavy tank managed to block the advance of elements of the 6th Panzer Division , which had established bridgeheads on the Dubysa . It stalled the German advance for a full day while being attacked by a variety of anti - tank weapons , until it finally ran out of ammunition . Tank versus tank engagements . Historians initially believed the new tanks were " scattered " among the army in small numbers , but recent scholarship identifies the exact opposite . The new tanks had been produced in large numbers , and concentrated into a dedicated type of formation , mechanized corps . Among the mechanized corps ( MC ) , four formations were especially well equipped ; on the day of German invasion , about 70 % of the total T - 34 and KV tanks produced at that time were deployed in the 6th , 4th , 8th , and 15th MC . The 6th MC operated in Białystok area , and all of the others in the Soviet Ukraine . All of their engagements with German tanks happened during or just before the Battle of Brody ( 1941 ) : Tank - to - tank battles were rare at the beginning of operation Barbarossa as Germans did not seek them ; they preferred to bypass the Soviet armor when possible . The two standing - out formations , 4th and 6th MC , lost almost all of T - 34 and KV tanks during movement , not coming under any German attack . Both corps tried to assemble counterattacks against German infantry ( not against panzers ) , but the counterattacks had no impact and were barely noticeable . Same pertained to the 15th MC after 26 June . In the first two weeks of invasion , the Soviet Union suffered the loss of most of its T - 34 and KV tanks , as well as the loss of most of the older tanks : On one hand , these corps had within weeks lost most of their T - 34 and KV tanks , but on the other hand , German reports did not note such a massive elimination in combat . The number of non - combat losses was unprecedented . German anti - tank capability . In the first weeks of the invasion , the main German anti - tank weapon was the 3 . 7 cm Pak 36 gun . The new 5 cm Pak 38 gun had just begun to enter service in small numbers , with a maximum of two guns per infantry regiment . Both types were practically useless against the T - 34 . German tanks of the time used similar types of guns , ineffective against the armor of new Soviet tanks . Generally the T - 34 clearly outclassed the existing Panzer III and Panzer IV medium tanks . Attempts to destroy the T - 34 and KV tanks concentrated on first immobilising them by firing at their tracks and then by tackling them with field artillery , anti - aircraft gun s , or by blowing them up at close range by shaped charge grenades . Impact on tank design worldwide . At the insistence of General Heinz Guderian , a special " Panzerkommision " arrived on 20 November 1941 on the Eastern Front to assess the T - 34 . To respond to the Soviet tanks , the Germans were forced to adopt new , heavier designs such as the Panther and Tiger , which in turn forced upgrades to the Soviet , United States and British tank fleets .