In 1884 a torpedo boat displacing 10 tons, with steam up, coal in the bunkers and a speed of 20.5 knots was thought to be impossibility. However, in 1894 Yarrow and Co. of Poplar produced the world's first aluminium torpedo boat (length 60 feet, beam 9 feet 6 inches), fitted with an inverted-vertical triple-expansion condensing marine engine, operating at 580 to 600 revolutions per minute, with steam supplied at 185 pounds per square inch by a Yarrow water-tube boiler with forced draught firing at two and a half inches of water gauge in the stokehold, and directly coupled to an aluminium bronze propeller. This second-class torpedo boat built for the French Government was designed for scouting purposes, and was capable of being carried on the deck of a large man-of-war, from which it could be lowered into the water when necessary. Lightness of construction was of paramount importance in such a vessel, because reduced displacement increased speed, and also reduced the load on the lifting gear used to raise and lower the vessel. A savings of about two tons in weight and a gain in speed of three and a half knots over vessels of the same class and dimensions in the British Navy was achieved. As little was known about the use of aluminium as a structural material at the time, Yarrow and Co. of Poplar, carried out a series of elaborate experiments on the metal to determine its working characteristics and corrosion resistance.