U-73 and the persistence of submarine-laid mines

U-73 was a Type UE I ocean-going submarine adapted for minelaying while retaining torpedo tubes and an 88 mm deck gun. She carried 38 mines and four torpedoes, with both torpedo tubes offset to starboard. Several Mediterranean minefields, probably including those that sank HMS Russell and Britannic, are attributed to the boat, although individual mine attribution remains uncertain. A minefield can threaten an enemy for weeks or months after the submarine leaves, extending the effect of a brief operation. One proposed future use of uncrewed underwater vessels is to lay such fields without revealing the parent submarine's position. Persistent machinery trouble eventually limited U-73, and her crew scuttled her at Pola in October 1918.