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The summer of 1936 saw the beginning of the assembly of six pre-production planes, which received the designation He 111C-0. By the end of 1936 all six C-0's had been built, each aircraft received its own name:
After being used for a short time on local routes, DLH declared that the He 111C was too expensive, and not economical. The He 111C program was cancelled and all six pre-production C-planes were passed on to the "Prestigious Routes" Berlin-Hanover-Amsterdam, Berlin-Nuremberg-Munich, and Cologne-Dortmund-Berlin. Later on He 111C-01 and He 111C-05 were used as special courier planes in the Southern Atlantic.
In mid-1937 He 111C-03 was passed to a secret reconnaissance unit named "Commando Rowehl", commanded by Oberstleutinant Theodore Rowehl. It was a special photographic reconnaissance unit, whose aircraft bearing civil registration performed clandestine photographic sorties over Britain, France and the Soviet Union.
During WWII the number of DLH's commercial routes were minimal. The He111C as well as another transport version, the He111G, was still used on the Berlin-Danzig-Konigsberg line, and only a few times on the Moscow-Berlin route. Just after the invasion of Poland all DLH's He111C's and He111G's were to be taken over by the Luftwaffe. These planes were fitted with military radio equipment and defensive armament. In the next few years the He111C was used as a liaison aircraft for general Luftwaffe needs.