The Italians were allowed to build 35,000 tons of capital ships each year during 1927 to 1929 under the terms of the Washington Treaty.
Initially a 23,000 ton design with 13.5" guns was proposed but when the French started construction on the Dunkerque it was found to be too small. Umberto Pugliese was the designer.
Initially it was thought to mount 16" guns but there were already 15" guns available from the cancelled Caracciolo class battleships.
The Littorio and Vittorio Veneto were ordered under the 1934 Program. The Roma and Imperio were ordered under the 1937 / 1938 Program.
To launch the three Ro.43 floatplanes was a single / two catapult. However sometimes a Re.2000 fighter was substituted, but as it was a land aircraft it couldn't be recovered.
The main guns were 15" L/50 M1934 built by Ansaldo and OTO. They could fire a 885 kg / 1,951 lb shell at 2,800'/sec / 2,854'/sec out to 46,216 yards / 46,800 yards at an elevation of 35°. The turrets weighed 1,560 tons / 1,570 tons.
The secondary battery were 6" L/55 M1934 built by Ansaldo and 6" L/55 M1936 built by OTO. They could fire a 110 lb shell out to 28,150 yards at 45°. The turrets weighed 133 tons.
There were twelve 3.5" L/50 M1938 built by Ansaldo or 3.5" L/50 M1939 built by OTO installed as the main anti-aircraft battery.
The secondary anti-aircraft battery consisted of twenty 37 mm L/54 Breda and sixteen 20 mm L/65 Breda guns.
There were two engine rooms that housed the turbines. These had the four boiler rooms in between.