This strange howitzer is the 1907 Krupp prototype designed for the future 15cm sFH 13 (that will be an hybrid between the Krupp and the RheinMetall protos tested in 1911), 4 of its kind being sold to Turkey in 1912. There are to surviving specimens, both captured in Palestine by the Australian Light Horse in 1917 or 1918.
This Canberra gun (serial Nr 19) identification (as for the Jamestown one - serial Nr 20) needed the help of several specialists.