Trento-class cruiser
The "Trento" class was a group of two heavy cruisers built for the Italian "Regia Marina" (Royal Navy) in the late 1920s, the first such vessels built for the Italian fleet. The two ships in the class— and , were named after the redeemed cities of Trento and Trieste taken from the Austro-Hungarian empire after the victory in World War I. The ships were very lightly armored, with only a thick armored belt, though they possessed a high speed and heavy armament of eight guns. Nominally built under the restrictions of the Washington Naval Treaty, the two  cruisers nevertheless exceeded the displacement limits imposed by the treaty. In the interwar period, the two cruisers served in the Cruiser Division, frequently alternating as the divisional flagship. "Trento" made two extensive trips abroad, the first was a tour of South American countries in mid to late-1929 and the second was a deployment to China to protect Italian nationals during the Chinese Civil War. In 1938, "Trieste" assisted in the repatriation of Italian volunteer soldiers who had fought in Spain during the Spanish Civil War. Both ships saw extensive action in World War II, including the battles of Calabria, Cape  Spartivento, and Cape Matapan. "Trieste" was damaged by a British submarine in November 1941 and therefore missed the First and Second Battles of Sirte, where at the latter action "Trento" damaged a British destroyer. "Trento" was torpedoed and sunk by a British torpedo bomber and a submarine in June 1942 with heavy loss of life. In April 1943, "Trieste" was also sunk in port at La Maddalena during an attack by United States heavy bombers. Salvage operations began in 1950, and after it was determined that the ship's engines had been preserved by leaked fuel oil, the hull was  sold to the Spanish Navy, which planned to convert the vessel into a light aircraft carrier. The plan was eventually cancelled in 1956 due to rising costs of the project, and "Trieste" was broken up for scrap in 1959. Design. In the early 1920s, the "Regia Marina" began design studies for cruisers that would adhere to the limitations of the Washington Naval Treaty, which limited cruisers to a displacement of and an armament of guns. The design for what became the "Trento" class was prepared by General Filippo Bonfiglietti in 1923. In 1924, the French Navy laid down the first  of two s, prompting the "Regia Marina" to order two vessels to match their rival. The designers emphasized very high speed, which required a significant reduction in armor protection to keep the ships within the displacement limit. In addition, they were designed with a narrow beam to help them reach high speeds, which reduced their stability. This would be the general pattern for Italian cruisers and destroyers built in the 1920s and 1930s, with the exception of the later s and some of the later s. While the ships were still on the slipways, officers in the "Regia Marina" expressed  concerns that the thin armor protection of the "Trento"s would leave the vessels poorly equipped for combat. As a result, the navy ordered the more balanced "Zara"-class, which featured a significantly thicker scale of armor protection. The lightly-built "Trento" design nevertheless provided the basis for the s built by Odero Terni Orlando for the Argentine Navy; the Argentine vessels were scaled down slightly, with thinner armor and guns. Another derivative design built for the Italian fleet, , started construction in 1930 and was commissioned in 1933; though the "Bolzano" was quite different from the other two vessels, she is sometimes  considered a member of the "Trento" class. General characteristics. The ships of the "Trento" class were long between perpendiculars and long overall. They had a beam of and a draft of . They had a design displacement of and they displaced up to at full load, though their displacement was nominally within the 10,000-long-ton restriction set in place by the Washington Naval Treaty. Their hulls had a flush deck and a bulbous bow, the first time the latter feature was employed on an Italian warship. The ships were completed with a pair of tripod masts, though on trials they  were found to vibrate excessively, and the foremast was strengthened with two extra legs. They had a crew of 723 officers and enlisted men, though during the war this increased to 781. They carried a pair of IMAM Ro.43 seaplanes for aerial reconnaissance; the hangar was located under the forecastle and a fixed catapult was mounted on the centerline at the bow. The "Trento"-class cruisers' power plant consisted of four Parsons steam turbines powered by twelve oil-fired Yarrow boilers, which were trunked into two funnels amidships. The boilers were divided into three boiler rooms with four each; two powered  the forward engines that drove the outboard propellers and the remaining four were allocated to the turbines that drove the center shafts. The engines were rated at for a top speed of , with projected service performance of for at normal displacement. On sea trials, "Trieste" only reached and "Trento" managed slightly less than that; these speeds could only be reached on a very light displacement, and in service, her practical top speed was only . The ships had a storage capacity of of fuel oil, which provided a cruising range of at a speed of . During refits in early 1940, funnel  caps were added to reduce smoke interference with the masts. Armament and armor. "Trento" and "Trieste" were armed with a main battery of eight Mod 24 50-caliber guns in four gun turrets; each turret carried the guns in a single cradle rather than independent mounts. The turrets were arranged in superfiring pairs forward and aft, and allowed for elevation to 45 degrees, for a maximum range of . They had a rate of fire of three rounds per minute, and the guns had to reset to 15 degrees to reload. The turrets were electrically operated, including the training and elevation  gear and the ammunition hoists. The guns suffered from excessive shell dispersion, like many other Italian guns of the period. Initially supplied with shells fired at a muzzle velocity of , the shells and propellant charges were reduced—to at —in an unsuccessful attempt to tighten shell grouping. The problem was in large part due to poor quality control in Italian munition factories, which failed to ensure tight manufacturing tolerances necessary for accurate shells. In addition, the single cradle mounts required the guns to be very close together; this caused the shells to interfere with each other in flight and contributed  to the dispersion problem. Fire control was provided by a pair of Barr & Stroud coincidence rangefinders. Anti-aircraft defense was provided by a battery of sixteen 47-cal. guns in twin mounts, four Vickers-Terni 40 mm/39 guns in single mounts and four machine guns. The 100 mm guns were copies of Austro-Hungarian guns designed in 1910 by Škoda that were placed in newly designed dual-purpose mounts that elevated to 85 degrees for a maximum range of . In addition to the gun armament, they carried eight torpedo tubes in four deck mounted twin launchers. The ships' secondary batteries  were revised several times during their careers. Both ships had their 100 mm guns replaced with newer Mod 31 versions of the same caliber. In 1937–1938, the two aft-most 100 mm guns were removed, along with all four 12.7 mm machine guns; eight 54-cal. Breda M1932 guns and eight Breda M1931 machine guns, all in twin mounts, were installed in their place. In 1942, "Trento" received four 65-cal. Breda M1940 guns in single mounts, with "Trieste" receiving eight of those guns the following year. Both vessels were protected with an armored citadel that covered the ships' vitals , including the machinery spaces and ammunition magazines. The vertical armored belt was thick and ran from forward of the fore main battery turrets to aft of the rear turrets. Either end of the belt was capped with armored bulkheads thick on the upper portion; the forward bulkhead had a lower section that was reduced to , and the aft bulkhead's lower portion was reduced to . Their armor deck was 50 mm thick in the central portion of the ship and reduced to aft, with thick sloped sides. The armor deck did not extend forward of the citadel. The gun turrets  had thick plating on the faces and the supporting barbettes they sat in were 70 mm thick above the armor deck and 60 mm thick below. The main conning tower had 100 mm thick sides and a 50 mm thick roof; above the tower was a fire control director with thick sides and a 60 mm thick roof. Service history. "Trento" and "Trieste" were named for the two largest unredeemed cities taken from Austria-Hungary in the aftermath of World War I. They frequently served as the flagship of the Cruiser Division throughout the 1930s. During the pre-war period , "Trento" made lengthy trips abroad, including a tour of South America from May to October 1929 and a deployment to China from January to June 1932 to protect Italian nationals during the Chinese Civil War. Both vessels took part in numerous naval reviews held for visiting foreign leaders in the 1930s, including Adolf Hitler of Nazi Germany and Miklós Horthy, the Regent of Hungary. In 1938 "Trieste" helped transport soldiers of the "Corpo Truppe Volontarie" (Corps of Volunteer Troops), which had been sent to Spain to fight in the Spanish Civil War, back to Italy. After Italy entered World War  II in June 1940, "Trento" and "Trieste" saw extensive action against British forces in the Mediterranean Sea, including at the battles of Calabria, Cape Spartivento, and Cape Matapan in July and November 1940 and March 1941, respectively. "Trento" was present at Calabria, where she battled British cruisers but did not sustain any damage. At the Battle of Cape Spartivento, either "Trento" or "Trieste" scored a hit on the British cruiser , and "Trieste" was briefly engaged but not seriously damaged by the battlecruiser . At Cape Matapan, the two cruisers engaged several British cruisers at very long range, with neither side scoring  any hits. In November 1941, "Trieste" was torpedoed by the submarine ; she spent most of the next year under repair. In the meantime, "Trento" was also present during the inconclusive First and Second Battles of Sirte, and at the latter she severely damaged a British destroyer. Both cruisers were also frequently tasked with escorting convoys to supply Italian forces in North Africa as well as interdicting British convoys to the island of Malta in the central Mediterranean. During one of the latter missions to attack the British Operation Harpoon convoy in June 1942, "Trento" was torpedoed twice, first by a  Bristol Beaufighter torpedo bomber and then sunk by the submarine with very heavy loss of life on 15 June; out of a wartime complement of 51 officers and 1,100 enlisted men, 549 were killed in the sinking, and a further 21 later died of wounds. "Trieste" returned to action in August 1942 for an operation that was cancelled following the torpedoing of another Italian cruiser by a British submarine. "Trieste" was moved to La Maddalena, Sardinia, where she was later sunk by United States heavy bombers on 10 April 1943. Salvage work on "Trieste" began in 1950. Her superstructure was  cut away and she was refloated and towed to La Spezia; an inspection revealed that fuel oil had leaked into the machinery spaces, protecting them while the ship had been submerged. The Spanish Navy purchased the hull in 1952 and had her towed to Ferrol, with plans to convert the vessel into a light aircraft carrier. The project ultimately came to nothing due to the growing costs of the project, forcing its cancellation in 1956. She was ultimately broken up by 1959.