Walther Forstmann (9 March 1883 – 2 November 1973) was one of the most highly decorated U-boat commanders in the Kaiserliche Marine during World War I. He also served in the Kriegsmarine during World War II in different staff positions. In his time as commander of U-12 and U-39 in World War I, he conducted 47 patrols and succeeded in sinking 148 ships for a total tonnage of 390,797 gross register tons (GRT). As such, he is the second most successful submarine commander ever (by tonnage sunk), after de la Perière.