Marcello-class submarine

German submarine UIT24 in the Inland Sea, Japan, August, 1944. UIT24 was the ex-Italian submarine Comandante Cappelini and was later the IJN I-503.
Class overview
Operators:	Regia Marina  Kriegsmarine  Imperial Japanese Navy
In commission:	1938–1947
Completed:	11
Lost:	10
Scrapped:	1
Preserved:	0
General characteristics
Type:	Submarine
Displacement:	1,060 long tons (1,080 t) surfaced 1,313 long tons (1,334 t) submerged
Length:	73 m (239 ft 6 in)
Beam:	7.19 m (23 ft 7 in)
Draught:	5.1 m (16 ft 9 in)
Propulsion:	Diesel-electric 2 × CRDA diesels (first 9 vessels) 2 × Fiat diesel engines (last 2 vessels) 2 × CRDA electric engines (all vessels)
Speed:	17.4 knots (20.0 mph; 32.2 km/h) surfaced 8 knots (9.2 mph; 15 km/h) submerged
Range:	2,500 nmi (4,600 km) at 17 knots (31 km/h) surfaced 7,500 nmi (13,900 km) at 9.4 knots (17 km/h) surfaced 8 nmi (15 km) at 8 knots (15 km/h) submerged 120 nmi (220 km) at 3 knots (6 km/h) submerged
Test depth:	100 m (330 ft)
Complement:	58
Armament:	8 × 533 mm (21 in) torpedo tubes (4 bow, 4 stern) 2 × 100 mm (3.9 in)/47 guns 4 × 13.2 mm (0.52 in) machine guns

The Marcello-class was a class of nine submarines built in 1937 and 1938 by CRDA in Trieste for the Royal Italian Navy (Italian: Regia Marina). 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 Provana's 1940 sinking, the remaining boats were transferred to the German submarine base (BETASOM) at Bordeaux in August 1940. After four boats had been sunk in the Atlantic, Barbarigo and Comandante Cappellini (sometimes also called Cappellini) 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 Dandolo was in operational condition at the end of the war.

Marcello (pennant number ML) was launched 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.