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

Germania B 1915
  Orthodox wood and fabric aircraft with ply-skinned fuselage. Several aircraft were built and used by the firm's flying school. Engine, 120 h.p. Argus As II.

M.Dusing Germania Flugzeugwerke and its Aircraft (A Centennial Perspective on Great War Airplanes 41)

B.I Biplane (Trainer)

  This training aircraft from 1914/15 is a two-bay, two-seat biplane with a plywood fuselage. This two-seater was equipped with a 120 hp Argus As II.
  Several Germania B.I aircraft were built, but neither the exact number nor the military units to which they were assigned are known. Matching statements prove that above all the Imperial Navy airmen were supplied. These were exclusively land planes. In the German Military Number Index are listed the designations: B.1050-1051/14 "Rahtjen B". These two aircraft finally went to the Navy, where they received the designations S.136 and S.137 (even before the changeover to the new L-number system). For sure these unarmed 2-seaters were used by the Freiwilligen Marinecorps (Volunteer Marinecorps) in Johannisthal or on its training field, the Bornstedter Feld near Potsdam.(1) The Imperial Navy only had this one central land flying training squadron at that time. Other land aviation units, especially the defense squadrons for the defense of naval bases and airship bases, but also other flight training squadrons, were not established until 1916.
  Perhaps early in 1916, the company launched an improved version of the aircraft designated KDD (Kampf-Doppeldecker). This reconnaissance aircraft differed from the B.I. by its wing design, a more powerful 150 hp Benz Bz III engine and a Parabellum 7.92 mm machine gun mounted on a movable turret in the rear cockpit.

(1) It is possible that the two Rahtjen aircraft did not receive their military numbers until then. They belonged to the last military numbers of 1914, which could possibly be related to the fiscal year of the military (01.04. to 31.03. of the following year). Possibly these were also the first Germania biplanes (type B.I), which were taken over/commissioned at the beginning of 1915 under the name Rahtjen, which can be explained by the fact that the formal renaming from Rahtjen to Germania was only carried out at the end of 1915.