of the total of 18,800 tons of vital rubber sent to Germany was shipped in May and June 1941. 2,100 tons of it crossed the border only hours before the German invasion began. Hitler breaks the Pact Initial invasion On June 22, 1941, Germany began Operation Barbarossa, the invasion of the Soviet Union through the territories that the two countries had previously divided. Because it had planned to attack the Soviet Union since late 1940, Germany managed to avoid delivery of about 750 million Reichsmarks of goods it was to have delivered under the economic agreements. This, however, cost Germany about 520 million Reichsmarks in counter-deliveries that the Soviets may have made before the invasion. Shortly before the June 22 attack, German ships began leaving Soviet harbors, some without being unloaded. That night after the invasion, Germans ferried out their remaining workers on the Lützow project, and Soviet naval workers let them go. After the launch of the invasion, within six months, the Soviet military had suffered 4.3 million casualties and Germany had captured three million Soviet prisoners, two million of which would die in German captivity by February 1942. German forces had advanced , and maintained a linearly measured front of . Soviet neutrality between 1939 and 1941 helped Germany to avoid a two front war. In 1941 Germany concentrated most of the Wehrmacht eastward in 1941, while continuing Soviet imports to Germany would prove vital to the German invasion of the Soviet Union. Ironically, despite fears causing the Soviet Union to enter deals with Germany in 1939, that Germany came so close to destroying the Soviet Union was due largely to Soviet actions taken from 1939 to 1941. Soviet raw materials supplies had helped convince German generals, who previously had refused to even discuss a Soviet invasion, to go along with Hitler's plans. Soviet imports into Germany, especially oil, proved essential for the Wehrmacht's conduct of the coming invasion. Without Soviet imports, German stocks would have run out in several key products by October 1941, within three and a half months. Germany would have already run through their stocks of rubber and grain before the first day of the invasion were it not for Soviet imports: {| class=wikitable |- ! !!Tot USSRimports ||June 1941German Stocks||June 1941 (w/oUSSR imports) ||October 1941German Stocks||October 1941 (w/oUSSR imports) |- style="text-align:center;" | align="left"|Oil Products||912||1350||438||905||-7 |- style="text-align:center;" | align="left"|Rubber||18.8 ||13.8 ||-4.9 ||12.1||-6.7 |- style="text-align:center;"