An item referred to the Rivista Marittime dated July/August 1938 which published an article written by colonel of naval weapons Bianco di San Secondo in which he made clear why 15,2cm/6” gun were to preferred above the 20,3cm/8” gun as main armament for a cruiser. He did not deny that a hit by a 20,3cm shell could cause much more damage than a 15,2cm shell. But it all depends on what was the target. That were in fact merchant ships, light units below the 3.000 ton and cruisers with an armour of just 6cm or with only the vital parts protected (by 1015cm). The high explosive shell was just effective against armour with a maximum thickness of 30cm regardless a calibre of 6” or 8”. While a 6” gun had a larger rate of fire was she even more effective than a 8” gun. Using shells suitable for penetrating armour was on a longer distance the 8” gun more effective, dealing with a thickness of 6cm no difference but with a thickness of 10cm and more was a 6” shell just able to penetrate on short distance from the opponent. The maximum range of a 6” gun was 25 and that of a 8” gun 30 kilometres. But still the rate of fire of a 6” was higher, a larger number was better for the fire control, easier to man and mechanical problems were less fatale than with 8” guns. Reckoning that a 6” gun had 75% of the score of a 8” guns he calculated the several options with as main conclusion that the main armament of a cruiser should be 6” and not 8“. The 5x3 gun arrangement was the most promising with the highest probably score.
With a 5x3-15,2cm/6” gun arrangement was the weight of the armament 750 tons, broadside weight salvo 750 kilo’s and a fire rate of 5 was it possible to fire 75 shells in a minute or every minute 3.750 kilo’s. Weight ammunition at 100 respectively 150 and 200 shots was 150, 225 and 300 tons. Weight armament and ammunition at 100 respectively 150 and 200 shots was 900,985 and 1.050 tons. Probable number of hits 56,25.
With a 5x3-15,2cm/6” gun arrangement was the weight of the armament 750 tons, broadside weight salvo 750 kilo’s and a fire rate of 5 was it possible to fire 75 shells in a minute or every minute 3.750 kilo’s. Weight ammunition at 100 respectively 150 and 200 shots was 150, 225 and 300 tons. Weight armament and ammunition at 100 respectively 150 and 200 shots was 900,985 and 1.050 tons. Probable number of hits 56,25.
