German army in 1939-1942 and many variants used its chassis, including the Hetzer, a tank destroyer with a 75mm gun. Despite its obsolescence, the Panzer I was also used in the invasion of France in May 1940. Of 2,574 tanks available for the campaign, no fewer than 523 were Panzer I's. There were only 627 Panzer III and IV medium tanks. At least a fifth of Germany's armor was composed of Panzer I's, while almost four-fifths was light tanks of one type or another, including 955 Panzer II, 106 Czech Panzer 35(t), and 228 Panzer 38(t). The French Army had up to 4,000 tanks, including 300 Char B1 heavy tanks, armed with a 47-mm (1.7 in) gun in the turret and a larger 75-mm (2.95 in) low-velocity howitzer in the hull. The French also had around 250 Somua S-35, widely regarded as one of the best tanks of the period, armed with the same 47 mm main gun and protected by almost of armor at its thickest point. The French forces also included over 3,000 light tanks, of which 500 were World War one-vintage FT-17s. The two main advantages German armor enjoyed were radios allowing them to coordinate faster than their British or French counterparts and superior tactical doctrine. The last major campaign in which the Panzer I formed a large portion of the armored strength was Operation Barbarossa, 22 June 1941. The 3,300 German tanks included about 410 Panzer I's. By the end of the month, a large portion of the Red Army found itself trapped in the Minsk pocket, and by 21 September Kiev had fallen, thereby allowing the Germans to concentrate on their ultimate objective, Moscow. Despite the success of Germany's armor in the Soviet Union, between June and September most German officers were shocked to find their tanks were inferior to newer Soviet models, the T-34 and Kliment Voroshilov (KV) series. Army Group North quickly realized that none of the tank guns currently in use by German armor could penetrate the thick armor of the KV-1. The performance of the Red Army during the Battle of Moscow and the growing numbers of new Soviet tanks made it obvious the Panzer I was not suitable for this front. Some less battle-worthy Panzer I's were tasked with towing lorries through mud to alleviate logistics problems at the front. In the Western Desert, the British Operation Compass pushed Italians