Grillo-class boats and harbour obstacles

Built for an attack on Pula, the Grillo class carried two lightweight torpedoes but made only about four knots on ten horsepower. Their tracks were intended to haul the boats over booms, chains, sandbanks, and other harbour obstacles that blocked an ordinary torpedo craft. The concept traded speed, armament, and open-water usefulness for the chance to penetrate a defended anchorage at night. The design shows how the Adriatic blockade and one highly specific operational problem could drive an otherwise improbable machine. Comparing it with the unchosen alternative of producing more aircraft for an aerial torpedo attack makes the Italian institutional choice as revealing as the engineering.