SM U-24 was one of 329 submarines serving in the Imperial German Navy in World War I. She was engaged in commerce warfare during the First Battle of the Atlantic.

In seven patrols, U-24 sank a total of 33 merchant ships and 1 auxiliary warship totalling 106,122 GRT and one warship for 15,000 tons, damaged three merchant ships for 14,318 GRT, and took one merchant ship as prize of 1,925 GRT.

Her second kill was the most significant. The victim was HMS Formidable, torpedoed 30 nautical miles (56 km; 35 mi) south of Lyme Regis, at 50°13′N 03°04′W / 50.217°N 3.067°W / 50.217; -3.067. She was hit in the number one boiler room on the port side. Out of a crew of approximately 711 men, 547 died as a result. This was one of the largest ships sunk by U-boats during the war.

In 1915, U-24 claimed another noted victim, the passenger steamer Arabic, causing 44 deaths, including three Americans. Arabic sank in 10 minutes. This escalated the U-boat fear in the U.S. and caused a diplomatic incident which resulted in the suspension of torpedoing non-military ships without notice.