Zara Class Cruiser (Italy) - Design

Design

The Zaras were essentially an improved Trento class tasked with dealing with the latest French designs.

The Trentos had been designed to the limitations of the Washington Naval Treaty, which stated that cruisers had to be 10,000 tons or less, and armed with 8-inch (200 mm) guns or smaller. The weight limitation made it impossible to design a ship with those guns and armour able to stop shells of the same caliber. A typical Washington design had 76 mm in its armour belt, and less on other areas of the ship. These thicknesses were reasonably good against destroyer and light cruiser weapons (typically between 5 in {127 mm} and 6 in {150 mm}), but insufficient against the 120 kg shells that 203 mm fired, capable of piercing even 150 mm at medium range. In general, in order to be effective, armour should be roughly the same thickness as the diameter of the shells fired against it.

Trentos had sacrificed armor for speed, allowing them to make high-speed dashes up and down the long Italian coastline, which would otherwise be difficult to defend from Italy's widely separated naval bases. Although equipped with powerful armament, hits against them would likely penetrate the armour and knock the ships out of combat. Even a won battle might seriously deplete Italian naval strength, something they were not prepared to address through sheer numbers.

The solution was a new design, one combining the armament of the Trentos with the armour needed to protect them from similar French designs. To achieve this, the Zaras were almost 2000 t (at standard displacement) over the 10,000 ton limit, even if fully loaded (because the modest amount of the fuel load) they displaced no more than, for example, British heavy cruisers. Extras such as a high superstructure and torpedo tubes were removed in an effort to save weight, but in the end the ships ended up considerably "overweight" anyway. The removal of the superstructure made placement of radar difficult, and in the end none of the class would ever carry one. This would prove to be a fatal omission.