On fifty days in the period, an average of eight divisions were in the line but fewer than six battalions attacked and only twice were more than half of the battalions in the line engaged simultaneously. British assaults were constant, small and narrow-front, against which the Germans could concentrate artillery, easily to inflict many casualties. British divisions stayed in the front line from and casualties varied from day in the 5th Division to fewer than day in the 23rd Division. Sheffield wrote that criticism of Haig underestimated the difficulty in balancing tactical, operational and strategic demands; line straightening attacks were costly but were better than imposing complicated manoeuvres on the infantry.