Armour, machinery, range, and guns

Portland improved belt protection over the Northampton class while retaining four geared turbines, four shafts, about 107,000 indicated horsepower, and a top speed near 32.7 knots. The design combined nine eight-inch guns with a stated cruising range of roughly 13,000 nautical miles at 15 knots. It remained an evolution of the existing scouting-cruiser formula. Coming closer to the treaty displacement limit used more weight than the Northamptons, yet the extra armour was still insufficient for fighting other eight-inch cruisers.