The Cannone da 90/50 Ansaldo Model 1938 and OTO Model 1939 had an autofretted monobloc barrel with a screwed-on breech ring containing the horizontal sliding breech block and seatings for the recoil and run-out cylinders. The most interesting part of the weapon was the single quadriaxal mounting designed for it: those were pre-stabilized, with a complex system controlled by 11 gyros, with two electric motors providing the necessary RPC; the whole complex was enclosed in an oval shielded turret, mainly to protect it from the blast effects from the battleship's main caliber guns. The turret weighed some 20 tons, and the practical rate of fire was 12 rounds per minute. After testing on the armoured cruiser "San Giorgio", the 90/50 was fitted on the new "Littorio"-class battleships and the two "Andrea Doria"-class battleships being rebuilt, for a respective total of 12 and 10 mountings.