Landships II

Please note the differences of the two portage trailers for the piece.  You will note the example in the Bulgarian collection is a single axle trailer, while the Greek fahrpanzer is carried on a samll wagon with forward turn wheels.   I believe the latter to be of commercial export design. While the former is exactly the type found in all war-time photos of the weapon system in German service  that I have seen. 

I might add that the KuK also used the fahrpanzer.  Though the weapon is exactly the same piece, the armor is of a different design.  It is interesting to note that Gruson was a principle contractor when the Austrians rebuilt the Przemysl forts in the 1890s.  though armament of the 19 forts was primarily 7,5cm, and 15cm cupola guns,  a number of these mobile gun systems were provided to the 23 smaller field works that formed the perimeter of the fortress.

In KuK servide it was termed: 6cm Fahrpanzerkanone M.98.