Various Battlecruiser Design Studies, c1916
These rough sketches outline the various arrangements being considered for construction. None were built, though some may have influenced the design of some ships who were started before the end of the war.
Most unusual amongst them is Umbau GrosseKreuzer Ersatz A, which seems to depict a reconstruction of one of the unfinished capital ships as a passenger ship.
"Shipcollector" writes from Germany to note:
The description on the plan is "Umbau Gr. Kreuzer Ers. A als Fracht- und Passagierdampfer" That translates as "Conversion large cruiser Replacement A to freight- and passengersteamer."
Peter Klein writes to add:
These design-studies were about the future all-big-gun-shipbuilding of the German Navy. The origin was a demand of the Emperor end of 1915 following a discussion about the replacement of the sunk armored cruiser Prinz Adalbert, which should have been replaced by a modern Battlecruiser of 7 the times costs (one of the later Yorck's). Tirpitz and the fleet tried to reject this discussion during the war, cause of legal problems about the approval by the parliament and cause of capacity lacks (the engineers of the design-department were needed for submarine and small craft design and was short at all, cause the army drafted a lot of them since August 1914). Not at least this rejection was a reason for the dismissal of Tirpitz in spring 1916. His successor, v. Capelle, was more to the will of the Emperor and so shortly before Jutland a number of design-studies were discussed (GK1-3, improvements of the Mackensen-Type with 15" and L1-L3 improvements of the Baden-type, elongated and faster).
Michel Rozon points out how some ad-hoc measurement of the weapons on GK6 through GK12 seems to suggest that the guns were to be of the 38cm caliber and not the later 42cm design, a fact he felt was not wholly clear from the Breyer reference.