The last would be delivered by the end of July, however, deliveries were halted by the Flars in June as the 160 hp Daimler powered Lohner C.I was inferior to the Brandenburg C.I. As Lohner was unable to remedy this deficiency, the company was fined with a penalty, and eventually 23 of the 24 aircraft were delivered, being serialed 18.01 to 18.23. The aircraft was unsuitable for front service, and was issued as trainers to Fliegerersatzkompanie (Flek, pilot reserve company) No. 1, 4 to 9, 11 and 14 and two Schulkompagnien (training companies).
On September 22, 1916, the Flars signed a contract for seventeen aircraft of the advanced C.I Series 18.5 (also known as Type Jcr), that received the military serials 18.51 to 18.67. Still fitted with the 160 hp Daimler engine, it was of lighter but stronger construction and had simplified wings of shorter span. Prototype was a C.I Series 18 aircraft, s/n 18.24, that was later reserialed 18.51. (Hence the pictured aircraft was the first production example.)
The C.I Series 18.5 had an increased but still moderate performance, and therefore the type was also used for training, and issued to Flek No. 3, 5, 7, 9, 12 and 13. In March 1917 four aircraft, s/n 18.61 to 18.64, were fitted with a Type II VK machinegun and were used to protect the Versuchsflik (test squadron) at Aspern, Vienna. Some C.I Series 18 and 18.5 were used to test new equipment, including a Wolf engine muffler, which was tested in s/n 18.63. In July 1917, 36 C.I's were still listed, although not all operable.
C.I Series 18 (Jc)
C.I Series 18.5 (Jcr)