Paddles, screws, and the Rattler trials

Paddle steamers such as HMS Gorgon offered useful early propulsion but put large, vulnerable wheels where a warship might otherwise carry guns. The Rattler and Alecto trials formed a broader programme of comparison, not just the famous tug-of-war. Rattler also outpaced her rival around Britain, giving the Royal Navy more than one measure of the screw's value. Modern warships are too expensive and powerful for the same kind of risky physical comparison, while computer modelling offers a cheaper and safer alternative. Choices such as azimuth pods versus shafts or impellers versus propellers are also less disparate than paddle wheels versus screws. The screw's success mattered because propulsion was becoming part of the hull, armament, and damage-survivability problem rather than merely a source of speed.