Franco-Prussian War
The French breech-loading rifle, the Chassepot, had a far longer range than the German needle gun; 1,500 yards (1,400 m) compared to 600 yd (550 m). The French also had an early machine-gun type weapon, the mitrailleuse, which could fire its thirty-seven barrels at a range of around 1,200 yd (1,100 m). It was developed in such secrecy, that little training with the weapon had occurred, leaving French gunners with no experience; the gun was treated like artillery and in this role it was ineffective. Worse still, once the small number of soldiers who had been trained how to use the new weapon became casualties, there were no replacements who knew how to operate the mitrailleuse.

Q: Treating the mitrailleuse like what rendered it far less effective
artillery