Cavallini
a family of submarines

by Cristiano D'Adamo

Design and Construction

Since the creation of the first submarines, and not until the introduction of more revolutionary designs later in WW II and in the post-war period, submarines were made up of three distinct components: inner hull, outer hull, and superstructure.

The inner hull, also known as the pressure hull, was usually built of various cylindrical sections sealed at both ends by semispherical cups from which protruded the torpedo tubes. A second cylindrical area was positioned amidships and was enclosed in the cunning tower. The outer hull was the seaworthy external shape of the submarine designed for navigational qualities. Within this outer shell there were compartments utilized for the storage of fluids (ballast or oil), external ballast or compensation tanks, and very little unutilized space.

The superstructure was constructed on top, aft and forward of the hulls and giving the submarine a flat deck, a cruiser-like bow and a round stern. This part was usually completely open to the ocean and seawater drained through wide openings above the outer hull, or smaller cutouts placed along the whole profile.  The “Settembrini” class, which followed the “Mameli” had the shape of the hull improved, thus improving the navigational qualities of the vessel. Although larger (more displacement, longer and wider hull), the “Settembrini” class was capable of reaching 18 knots versus the 17.2 of the “Mameli”, even though they were sharing the identical power plant.
 

The Saint Bon under early construction. The circular beams are clearly visible.
(Photo Turrini)

All the “Cavallini” class submarines were of the saddle tank, or partial double hull design.   The “Mameli” class had a perfectly cylindrical pressure hull made of cylindrical beams (reinforcement rings) positioned 500 mm (19.69 in) apart and to which were riveted multiple steel plates positioned in a brick layer fashion (each plate tended to overlap the other half of the adjacent plates). Plates were made of nickel steel with a breaking point of 60 kg/mm2 (853.4 psi), and an enervating point of 42 kg/mm2 (597.4 psi).  Plates were 18 mm (0.7087 in) thick around midship and 16 mm (0.6299 in) thick toward the extremity.  The forward and aft sections were tapered so that the internal circumference of the supporting beams was larger in the central compartments than the extreme ones. Each plate was secured by a double row of rivets, and an extra plate was installed inside and outside of the riveted area.

The entire pressure hull was divided into five primary compartments plus the control room. Starting aft, the first compartment was the aft torpedo room which also included the electric motors, followed by the diesel engine rooms, the control room, the officer and petty officer quarters and first battery holds, and finally the forward torpedo room and the second battery hold. Above the control room there was a smaller chamber (conning tower). The two periscope sleeves were also considered parts of the pressure hull.

The two half spherical extremities of the Ammiraglio Caracciolo where are clearly
visible the opening for the torpedo tubes.
(Photo Turrini)

A watertight bulkhead capable of withstanding water pressures up to 40 atmospheres (853.4 psi) separated each compartment. Later evolutions of the “Cavallini” had this bulkhead reinforced.   The outer hull was made of 7 mm (0.2756 in) steel, and as already mentioned, the space in between the two hulls was used to stow diesel fuel and ballast water. On each side (in each saddle) there were two water tanks and a diesel fuel tank. The upper deck was surfaced with teak wood slats bolted to the metal frame.  The shape of the bow varied from class to class. The “Mameli” had a round bow and a sloped stern. The “Settembrini” had the bow redesigned in more geometrical lines. The same designed was kept on the “Archimede”, but the later classes returned to a round bow, while the “Liuzzi” also had an elongated stern.