O.Thetford, P.Gray German Aircraft of the First World War (Putnam)

Halberstadt C III
   Built towards the end of 1917, the C III was the first of the Halberstadt standard two-seaters intended for long-range reconnaissance, and formed the basis of the later C V, which was to see series production. It was a conventional machine of wood and fabric with ply-skinned fuselage; its only singular feature was the mounting of the lower wing on a keel to afford an increased gap. According to Idflieg report, six machines were completed. Engine, 200 h.p. Benz Bz IV. Span, 12.2 m. (40 ft. 0 3/8 in.) length, 7.7 m. (25 ft. 3 1/4 in.). Height, 2.95 m. (9 ft. 8 1/8 in.). Weights: Empty. 850 kg. (1.870 lb.). Loaded, 1.310 kg. (2,882 lb.). Speed, ca. 165 km.hr. (103.125 m.p.h.). Armament, one Parabellum and one Spandau machine-gun.

J.Herris Halberstadt Aircraft of WWI. Volume 1: A-types to C.III (A Centennial Perspective on Great War Airplanes 44)

Halberstadt C.III

  The first full-size C-type aircraft designed by Halberstadt was the Halberstadt C.III, which was brought out in the autumn of 1917. Halberstadt C.III 14655/17 (work no. 872) was powered by a 200 hp Benz Bz.IV engine. This was the same engine used in other contemporary C-types and not the high-altitude version of the engine used by the later C.V.
  The C.III was clearly influenced by the CL.II. In fact, it looked much like an enlarged CL.II with two-bay wings. A spinner was fitted for its type-test.
  The Halberstadt C.III proved so promising during its initial flight trials in early October 1917 that it was rushed to Adlershof for a preliminary type-test. This was unusual.
  On October 31 Idflieg reported short-range reconnaissance and artillery evaluation flights by the C.III had shown useful results, and stated that type-testing would take place in three to four weeks. In November additional short-range reconnaissance flights and artillery spotting flights were performed that also reported good results and a preliminary type-test was performed.
  Idflieg reported that on December 3 the 'new' C.III was flown to Adlershof to be present for initial discussions about type-testing. Three prototypes, one for flight testing, one for static testing, and a spare, were usually ordered, so this might have been another prototype or the modified first prototype.
  The C.III underwent static load testing on December 19 but the official type tests had not yet been performed. In January Idflieg stated that the type-test would take place on 2 February 1918.
  As a result of the type-test, Idflieg reported that there were some structural deficiencies, requiring modifications. More serious, the required climb rate was not achieved. Although Idflieg stated at the end of February that a structurally improved C.III would be delivered to Adlershof in about three weeks, no more was heard of the C.III.
  Instead, Halberstadt chief engineer Karl Theis designed the totally new Halberstadt C.V powered by the Benz Bz.IVu high-altitude engine. The C.V, which first flew in early March, demonstrated the excellent climb rate Idflieg was looking for and the C.III was abandoned.