Italian submarine Ondina

The Sirena class was an improved and enlarged version of the preceding Argonauta-class submarines. They displaced 691 metric tons (680 long tons) surfaced and 850 metric tons (837 long tons) submerged. The submarines were 61.5 meters (201 ft 9 in) long, had a beam of 5.7 meters (18 ft 8 in) and a draft of 4.7 meters (15 ft 5 in). Their crew numbered 45 officers and enlisted men.[1]

For surface running, the boats were powered by two 675-brake-horsepower (503 kW) diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 400-horsepower (298 kW) electric motor. They could reach 14 knots (26 km/h; 16 mph) on the surface and 7.5 knots (13.9 km/h; 8.6 mph) underwater.[2] On the surface, the Sirena class had a range of 5,000 nautical miles (9,300 km; 5,800 mi) at 8 knots (15 km/h; 9.2 mph);[1] submerged, they had a range of 72 nmi (133 km; 83 mi) at 4 knots (7.4 km/h; 4.6 mph).[2]

The boats were armed with six 53.3-centimeter (21 in) torpedo tubes, four in the bow and two in the stern for which they carried a total of 12 torpedoes. They were also armed with a single 100 mm (3.9 in) deck gun forward of the conning tower for combat on the surface. The anti-aircraft armament consisted of two or four 13.2-millimeter (0.52 in) machine guns.[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]

Refah tragedy in the daily newspaper Cumhuriyet on June 27, 1941

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.

Ondina was also sunk a year later by the warships English Protea, HMSAS Southern Maid and Walrus warplanes near Cyprus At (34-35 N, 34-56 E) on 11 July 1942. However, the command of Ondina was under Lieutenant Gabriele Adolfi at that time. The Italian sailors from Ondina were recovered by the warships. (5 killed/41 survived).[3]

• Bagnasco, Erminio (1977). Submarines of World War Two. Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-962-6.
• Brescia, Maurizio (2012). Mussolini's Navy: A Reference Guide to the Regina Marina 1930–45. Annapolis, Maryland: Naval Institute Press. ISBN 978-1-59114-544-8.
• Chesneau, Roger, ed. (1980). Conway's All the World's Fighting Ships 1922–1946. Greenwich, UK: Conway Maritime Press. ISBN 0-85177-146-7.
• Rohwer, Jürgen (2005). Chronology of the War at Sea 1939–1945: The Naval History of World War Two (Third Revised ed.). Annapolis, Maryland: Naval Institute Press. ISBN 1-59114-119-2.

• Sommergibili Marina Militare website