SM U-42 was a Pacinotti type submarine laid down on 18 August 1913 in Italy at Società Fiat-San Giorgio, Muggiano, La Spezia. Ordered by the Imperial German Navy the submarine was confiscated by the Italian government on 8 August 1915 after entering war with the Austria-Hungary. Commissioned as Balilla into the Regia Marina the submarine was sunk off Lissa by Austro-Hungarian torpedo boats 65 T and 66 T.