Black Swan speed and built-in modification margin

The Black Swan design gained only roughly one or two hundred tons over the Bitterns, yet incremental machinery changes produced a useful speed advantage. The Bitterns used two-shaft geared turbines rated at 3,300 shaft horsepower, while the Black Swan figure discussed is about 3,600 horsepower. Bitterns were designed for about 18.75 knots and made roughly 19 on trial, while Black Swans generally reached 19 to 20 knots. The corvettes discussed in the preceding episode apparently did not exceed 18 knots, even after modification. Speed was one expression of a wider design habit below cruiser size: smaller ships accumulated substantial changes during service, with motor torpedo boats and motor gunboats offered as the most extreme examples. Sloops were built with that process in mind, including the ability to remove the X mounting and use the released space for new weapons or equipment. Their combat value came from a stable hull that anticipated alteration rather than from one frozen armament plan.