Grillo-class tracked torpedo motorboat

The Grillo class was a class of torpedo-armed motorboats in service with the Regia Marina (the Royal Navy of Italy) during the First World War. The notable feature of these vessels was that each was equipped with a pair of spiked continuous tracks, intended to allow them to climb over harbour booms and attack enemy shipping at anchor. In 1918, two attempts to use them to penetrate Austro-Hungarian harbour defences both ended in failure.