The Iris-class ships were designed as dispatch vessels by William White under the direction of Nathaniel Barnaby, Director of Naval Construction, and were later redesignated as second-class protected cruisers.

[1] The ships were not armoured but extensive internal subdivision gave them some protection against flooding, as did the 150-foot-long (45.7 m) double bottom under the propulsion machinery compartments.

Each engine drove one propeller shaft using steam from eight oval and four cylindrical boilers with a working pressure of 65 psi (448 kPa; 5 kgf/cm2).

[1] The engines were designed to produce a total of 6,000 indicated horsepower (4,500 kW) for a speed of 17 knots (31 km/h; 20 mph), which was handily exceeded by the sisters.

[3] The ships carried a maximum of 780 long tons (793 t) of coal, enough to steam 4,400–4,950 nautical miles (8,150–9,170 km; 5,060–5,700 mi) at 10 knots (19 km/h; 12 mph).