normal atmospheric compressed air rather than pure oxygen. This significantly increased the range of the torpedo, the 24.5 inch Mk 1 having a range of at or at with a warhead. There was a general nervousness about the oxygen enrichment equipment, known for reasons of secrecy as 'No 1 Air Compressor Room' on board ships, and development shifted to the highly efficient Brotherhood Burner Cycle engine that used un-enriched air. Burner cycle engine After the First World War Brotherhood developed a 4 cylinder burner cycle engine which was roughly twice as powerful as the older wet heater engine. It was first used in the British Mk VIII torpedoes, which were still in service in 1982. It used a modified diesel cycle, using a small amount of paraffin to heat the incoming air, which was then compressed and further heated by the piston, and then more fuel was injected. It produced about 322 hp when introduced, but by the end of WW2 was at 465 hp, and there was a proposal to fuel it with nitric acid when it was projected to develop 750 hp. Wire driven The Brennan torpedo had two wires wound around internal drums. Shore-based steam winches pulled the wires, which spun the drums and drove the propellers. An operator controlled the relative speeds of the winches, providing guidance. Such systems were used for coastal defense of the British homeland and colonies from 1887 to 1903 and were purchased by, and under the control of, the Army as opposed to the Navy. Speed was about for over 2,400 m. Flywheel The Howell torpedo used by the US Navy in the late 19th century featured a heavy flywheel that had to be spun up before launch. It was able to travel about at . The Howell had the advantage of not leaving a trail of bubbles behind it, unlike compressed air torpedoes. This gave the target vessel less chance to detect and evade the torpedo and avoided giving away the attacker's position. Additionally, it ran at a constant depth, unlike Whitehead models. Electric batteries Electric propulsion systems avoided tell-tale bubbles. John Ericsson invented an electrically propelled torpedo in 1873; it was powered by a cable from an external power source, because batteries of the time had insufficient capacity. The Sims-Edison torpedo was similarly powered. The Nordfelt torpedo was also electrically powered and was steered by impulses down a trailing