A large number of steam pinnaces (length 56 feet, beam 9 feet 9 inches, depth 4 feet 7 inches; displacement 17 tons) fitted with inverted-vertical compound marine engines with the cylinders supported on turned steel columns well stayed together, and carrying the piston-rod guide-bars, operating with steam supplied by a Thames Ironworks water-tube boiler, were built by the Thames Ironworks Company, Blackwall, for the British Government. The pinnaces were armed with one 3-pounder quick-firing gun forward, one 0.45 inch Maxim machine gun aft, and two sets of side-dropping gear, for 14 inch Whitehead torpedoes.