High Quality Content by WIKIPEDIA articles! The development of the steam ironclad firing explosive shells in the mid 19th century rendered sailing tactics obsolete. New tactics were developed for the big-gun Dreadnought battleships. The mine, torpedo, submarine and aircraft posed new threats, each of which had to be countered, leading to tactical developments such as anti-submarine warfare and the use of dazzle camouflage. By the end of the steam age, aircraft carriers had replaced battleships as the principal unit of the fleet. The interval of ninety years between the end of the Napoleonic Wars in 1815 and the beginning of the Russo-Japanese War in 1904 was marked by no major naval war. There was fighting at sea, and there were prolonged blockades, but there were no campaigns between large and well appointed navies. During this period an entire revolution took place in the means of propulsion, armament and construction of ships.