SM U-38 was a German Type U 31 U-boat which operated in the Mediterranean Sea during World War I. It ended up being the third most successful U-boat participating in the war, sinking 134 merchant ships sunk for a total of 287,811 GRT. In 1917 Valentiner was succeeded as commander of U-38 by Kptlt. Wilhelm Canaris, who decades later became an Admiral and head of the Abwehr (German Military Intelligence), in 1935–1944.