SM U-42 was a submarine ordered for construction by the Imperial German Navy. The vessel was designed by the naval engineer Cesare Laurenti, and laid down on 18 August 1913 in Italy at Società FIAT-San Giorgio, Muggiano, La Spezia. It served as the basis for the design of the Pacinotti-class submarines. The vessel was confiscated by the Italian government after entering the World War I. The vessel was renamed Balilla and served with the Royal Italian Navy (Regia Marina) until sunk in a battle on 14 July 1916 with two torpedo boats.

Construction and career

Ordered by the Imperial German Navy as the U-42, the submarine was confiscated by the Italian government on 8 August 1915 after entering war with Austria-Hungary during World War I. The submarine was then completed and Commissioned as Balilla by the Regia Marina. After completion of trials, the Balilla was added to the 4th Squadriglia at Brindisi in February 1916, where it was tasked with guarding the coast against enemy forces as well as short-range ambush missions against enemy vessels. On 14 July 1916 she was attacked by two Kaiman-class torpedo boats, the Hydra and Skorpion. After a lengthy surface battle, Balilla was sunk by gunfire with all hands lost.