And when the Russians switched to the even better T-34/85, German tank losses really soared, even with the better German models coming by late 1942. It didn't help the Germans that the arrival of the Il-2 Sturmovik anti-tank attack plane in large numbers also resulted in heavy German losses.
In his autobiography the Panzer General Guderian wrote about taking a group of Soviet tank officers on a tour of the plants producing the Panzer III and Panzer IVs in early 1941. As a party to the Nazi-Soviet Pact of 1939, Hitler had agreed to share tank technology with the Soviets. Hitler order that that part of the treaty be strictly complied with, so a very reluctant Guderian showed off Germany's latest tanks to the Soviets. (Guderian did not know at the time that Hitler planned to invade and destroy the USSR before it had a chance to use the technology he was giving it).
When the tour was over the Soviet officers rudely accused Guderian of acting in bad faith, and demanded to be shown Germany's latest and best tanks. After listening to Guderian's truthful protestations that these were Germany's latest and best tanks, the unconvinced Soviet officers stormed off.
Guderian discussed the meaning of the incident with his fellow panzer officers and they decided that if the roles were reversed the Soviets would hide their best tanks, and the Soviet officers had simply assumed that Germany was doing so. Guderian said he was left with a nagging feeling that persisted until his men encountered the T-34 and he understood why the Soviets had assumed that the Panzer IIIs and IVs could not be Germany's best tanks.