All four ships incorporated a unique underwater protection system named after its designer, Umberto Pugliese. A 40 mm thick torpedo bulkhead extended inboard from the base of the main belt before curving down to meet the bottom of the hull. This formed a void which housed an empty drum wide with thick walls; the rest of the void was filled with liquid. The drum ran the length of the torpedo defense system, and was designed to collapse to contain the explosive pressure of a torpedo hit. The torpedo bulkhead would prevent any splinters or explosive effects from entering the ships' vitals. The system was designed to protect the ship from torpedo warheads up to .