The Rival Brothers' Patriotism(1911)

Two brothers, of good old New England stock. Love the same maid, but she loves one a great deal more than the other, so when war breaks out Jim decides to go, and is one of the first volunteers. His brother follows him almost immediately and the next few weeks are taken up in camp. Both brothers win favor and promotion and have a record for daring. Once when the mail arrived at camp, Jim gets a letter, opens it and reads what was never intended for his eyes. It is a love letter from the girl to his brother and he had opened it by mistake.