[1] For surface running, the boats were powered by two 675-brake-horsepower (503 kW) diesel engines, each driving one propeller shaft.

They were also armed with a single 100 mm (3.9 in) deck gun forward of the conning tower for combat on the surface.

[1] Ondina was laid down by Cantieri Riuniti dell'Adriatico at their Monfalcone shipyard in 1931, launched on 2 December 1933 and completed the following year.

[1] On 23 June 1941 Ondina under the command of Corrado Dal Pozzo at location indicated as (36.08N-34.44E) in Italian naval records.

Ondina and Italian Naval records show the submarine fired a torpedo and sank the Turkish Transport vessel Refah of whom only 32 survived out of 200 on board.