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i am not recognising the greek gun, probably a WWI 58 french trench gun which the french send in small numbers
the guns had the Hellenic army (Greek) before WWI was
Schneider field gun 7.5cm M1908 (in foreign sources refered as M1906)
Scneider-Danglis mountain M1908 (in foreign sources refered as M1906)
some old non QF Krupp guns from 1880s 8.7cm, 10.5cm and 15 cm
in the WWI the Entent send
Schneider ducrest 65mm
some 58mm trench gun (not know the type)
De Bange 120mm M1878
Vickers 6 inch gun cvw 30 M1897