The Marcello class was a class of nine submarines built in 1937 and 1938 by CRDA in Trieste for the Royal Italian Navy (). Two similar submarines built in 1939 at La Spezia by Oto Melara are sometimes considered part of the class. All eleven served in the Mediterranean Sea at the start of the Second World War. After s 1940 sinking, the remaining boats were transferred to the BETASOM Atlantic submarine base at Bordeaux in August 1940. After four boats had been sunk in the Atlantic, and were then selected for conversion to "transport submarines" in order to exchange rare or irreplaceable trade goods with Japan. Cargo capacity of 160 tons reduced reserve buoyancy from 20–25% to 3.5–6%; and armament was reduced to defensive machine guns. Only was in operational condition at the end of the war.
Class members
Marcello
(pennant number ML) was launched on 20 November 1937 and completed on 5 March 1938. When Italy declared war, Marcello was temporarily disabled by air conditioning system leaks. Leakage of chloromethane refrigerants during submerged operations had caused central nervous system poisoning of the crew. After unsuccessful patrols in the Mediterranean, Marcello sailed on 31 October 1940 and passed the Strait of Gibraltar on 5 November for an Atlantic patrol to Bordeaux on 2 December. Marcello sank one ship on its first BETASOM patrol and was lost to unknown causes on its next patrol in late February 1941.
Dandolo
Dandolo (pennant number DO) was launched 20 November 1937 and completed on 25 March 1938. After unsuccessful patrols in the Mediterranean, Dandolo sailed on 13 August 1940 and passed the Strait of Gibraltar on 16 August for an Atlantic patrol to Bordeaux on 10 September. Dandolo sank one ship and damaged another en route to Bordeaux. After an unsuccessful patrol, Dandolo sank one ship on its second BETASOM patrol. After another unsuccessful patrol, Dandolo sailed from Bordeaux on 26 June, passed the Strait of Gibraltar on 2 July, and returned to Naples on 7 July. Dandolo spent the remainder of the war in the Mediterranean damaging a neutral French tanker on 4 November 1941, sinking the neutral Spanish freighter Castillo Oropesa on 8 November 1941, and damaging the cruiser on 16 July 1943. Dandolo sailed to the United States after the Italian armistice, and was scrapped in 1948.
Mocenigo
(pennant number MO) was launched 20 November 1937. Mocenigo was sunk off Cagliari during a 13 May 1943 USAAF air raid.
Nani
(pennant number NI) was launched 16 January 1938. After unsuccessful patrols in the Mediterranean, Nani sailed on 29 September 1940 and passed the Strait of Gibraltar for an Atlantic patrol to Bordeaux on 4 November. Nani sank two ships en route to Bordeaux. Nani was lost to unknown causes sometime after 3 January 1941 on its first BETASOM patrol. j According to the Daily Telegraph obituary of Cpt Humphrey Boyes-Smith RN who died 24/6/99, Nani was sunk by depth charges from the Flower-class corvette HMS Anemone on 7/1/41.
Veniero
(pennant number VN) was launched 14 February 1938 and completed on 6 June. After an unsuccessful Mediterranean patrol, Veniero passed the Strait of Gibraltar on 7 July 1940 for an Atlantic patrol near the Canary Islands and returned past Gibraltar on 27 July. This was the first Axis submarine to pass Gibraltar during World War II, and the report of conditions delivered upon return to Naples on 1 August assisted future attempts to pass the strait. Veniero sailed on 28 September 1940 and passed the Strait of Gibraltar for an Atlantic patrol to Bordeaux on 2 November. After sinking two ships in six BETASOM patrols, Veniero sailed from Bordeaux on 8 August 1941 and returned through the Strait of Gibraltar to La Spezia on 2 September. On its seventh patrol after return to the Mediterranean, Veniero was assumed sunk (identification not confirmed) by a Consolidated PBY Catalina on 7 June 1942.
Provana
Provana (pennant number PR) was launched 16 March 1938. Provana was the first Italian submarine lost after Italy's declaration of war. Provana was sunk by the French sloop La Curieuse on 16 June 1940.