The Balilla-class were the first submarines to be built for the Italian navy following the end of World War I. They were large ocean-going cruiser submarines designed to operate in the Indian Ocean based in Italy's East African colonies. The design was double-hulled and based on the German Type UE 2 U-boats, one of which, U-120 was supplied to the Italians as a war reparation. A auxiliary diesel engine was installed as an extra generator.