The He111 was the German bomber that was built in greatest numbers during World War II; it was derived from a commercial aircraft dating back to 1936. By the end of summer 1939 the first He111 H-1 had left the Heinkel works in Oranienburg and in October 1939 they appeared on the front. The He111 squadrons were used primarily during the Battle of Britain and suffered heavy losses. Within the H series the H-6 played an outstanding role. With over 1600 machines built, it was the most numerous He111 after the H-16. Equipped with more powerful armament from the outset it was designed for used as a torpedo bomber against shipping targets. However it could also carry two heavy bombs of 1000 kg each on external racks under the fuselage. By the time production ended in 1945 a total of 6508 of these aircraft had been built in different versions.