Why the Amphions were more than modified Leanders

The Amphions developed the trade-protection cruiser toward a distinct hull and machinery arrangement. That design family divided between larger Town-type cruisers and smaller Arethusas that could be built in greater numbers. Two separated groups of boilers and turbines gave the Amphions their two funnels and reduced the chance of losing all propulsion to one torpedo. If a hit disabled one group's turbines and the other's boilers, cross-connections could supply the surviving turbines from the surviving boilers. Four higher-pressure Admiralty three-drum boilers generated the same 72,000 shaft horsepower as the Leanders' six boilers, while the revised hull extended cruising range to about 7,000 nautical miles at 16 knots. Although slightly longer and broader than a Leander, an Amphion displaced less while carrying a six-inch main battery, four four-inch anti-aircraft guns, machine guns, and eight 21-inch torpedoes. Magazine protection concentrated three-and-a-half inches of armour over the likeliest impact areas and two inches elsewhere, with additional protection for the deck and turrets.