SM U-30[Note 1] was one of 329 U-boat submarines serving in the Imperial German Navy in World War I.

U-30 is significant for the torpedoing of the US tanker Gulflight on 1 May 1915 20 nautical miles (37 km; 23 mi) west of Scilly.

A Dutch ship was stopped and, as a neutral, permitted to continue at a point some 45 nautical miles (83 km; 52 mi) north west of the Scilly Isles, but the submarine was spotted at this point by a steam drifter, Clara Alice which reported her position to a naval patrol.

[4] The patrol ships HMS Iago and Filey started to hunt for the submarine, but succeeded only in intercepting the US-flagged Gulflight, which they took under escort.

Although the United States remained officially neutral in the ongoing hostilities, it reached agreement with the German government that further attacks by submarine would be strictly in accordance with "cruiser Rules" as defined by international law.