This design is one of those realized by General Luigi Barberis, commissioned by Admiral Gino Ducci, Regia Marina’s Chief of Staff.
Barberis’ work was group in three set of studies:
- group one, units up to 14.000 tons, 147 to 205 meters length, 3 triple 203 mm. or 3 double 305 mm, 28 to 36 k speed;
- group two, units up to 20.000 tons, 169 to 228 meters length, 2 triple 305 mm. or 4 double 305 mm., 28 to 36 k speed
- group three, units over 26.000 tons.
The S4 design belongs to the group three, all the specs are reported on the drawing. With any evidence the space amidship was to be used for scout airplanes.
One of the few Regia Marina designs considering 406mmm for the main guns.
(Source: Progetti di corazzate per la Regia Marina, Michele Cosentino, Storia militare)