The battle began with the heavy bombing of the city by "Generaloberst" Wolfram von Richthofen's "Luftflotte 4", which in the summer and autumn of 1942 was the single most powerful air formation in the world. Some 1,000 tons of bombs were dropped in 48 hours, more than in London at the height of the Blitz. The exact number of civilians killed is unknown but was most likely very high. Around 40,000 civilians were taken to Germany as slave workers, some fled during battle and a small number were evacuated by the Soviets, but by February 1943 only 10,000 to 60,000 civilians were still alive. Much of the city was smashed to rubble, although some factories continued production while workers joined in the fighting. The Stalingrad Tractor Factory continued to turn out T-34 tanks up until German troops burst into the plant. The 369th (Croatian) Reinforced Infantry Regiment was the only non-German unit selected by the "Wehrmacht" to enter Stalingrad city during assault operations. It fought as part of the 100th Jäger Division.