Complete the following sentence: It is believed two mortars were used during the initial French operations to retake Fort Douaumont during the Battle of Verdun, attracting four mortars for the final assault. <unk> <unk> <unk> <unk> <unk> <unk>
Champagne region between August 1915-Feb 1916. Two were used during the Battle of Hartmannswillerkopf during 1915<unk>1916.