From the Dregs (1915)

Lieutenant Curren of the regular army, is assaulted by Private Roy, of his company, and the latter is sent to the military prison. Known as Convict 125, Roy serves a year of his time, then his desire for revenge turns to repentance and he apologizes to Curren. A pardon is secured and Roy reinstated in the service. War breaks out, and Roy saves the Lieutenant's life on the field of battle but loses his own in doing so. From a locket found on Roy, Curren's wife identifies him as her long-lost brother