Unknown Love.

Doris Parker, the daughter of an American Marine Officer, becomes Harry Townsend's pen pal. Harry is a young American soldier with no family who has gone to fight in France. As they exchange letters, Doris falls for Harry, despite advances made by Jack Tims, a captain of the Royal Navy training with the American Marines. On the front in France, Harry's face is wounded. Overwhelmed by the news, Doris asks Jack Tims to take Harry onboard a ship he is taking to France. During the voyage, Jack foils an attack from an enemy submarine but is wounded in the battle and dies.