HMS Iris was an Iris-class second-class cruiser of the Royal Navy. The Iris-class ships were the first all-steel ships to serve with the Royal Navy and were employed as armed dispatch vessels. She had a double bottom and her Maudslay machinery produced 7,300 hp (5,400 kW), slightly less than her sister ship HMS Mercury, but her 17.35 knots (32.13 km/h) still made her one of the fastest ships of her day. Mercury was identical in most respects, though she had an upright stem and a different arrangement of head sail.