The Constantinople Flotilla (German: U-Flottille Konstantinopel) was an Imperial German Navy formation set up during World War I to prosecute the U-boat campaign against Allied shipping in the Mediterranean and the Black Sea in support of Germany's ally, the Ottoman Empire. Despite its official name, the "U-boats of the Mediterranean Division in Constantinople" (U-Boote der Mittelmeerdivision in Konstantinopel), it saw little service there, operating mostly against Russian shipping in the Black Sea.