U-64 was a Type U-63 class submarine in the Kaiserliche Marine that served during World War I. She was built in 1916 and served in the Mediterranean Sea. On 19 March 1917, while on patrol in the Tyrrhenian Sea, U-64 encountered the French battleship Danton 30 miles south of Sardinia. U-64 torpedoed the Danton which sank in 45 minutes with the loss of 296 men. During her career, U-64 was under the command of Kapitänleutnant Robert Moraht. She was lost on 17 June 1918.