Penelope was powered by four Parsons steam turbines, each driving one propeller shaft, which produced a total of 40,000 indicated horsepower (30,000 kW).

The turbines used steam generated by eight Yarrow boilers which gave her a speed of about 28.5 knots (52.8 km/h; 32.8 mph).

[5] The main armament of the Arethusa-class ships was two BL 6-inch (152 mm) Mk XII guns that were mounted on the centreline fore and aft of the superstructure and six QF 4-inch Mk V guns in waist mountings.

In August 1915, she was assigned to the 5th Light Cruiser Squadron of the Harwich Force, guarding the eastern approaches to the English Channel.

She survived to the end of the First World War, and was sold for scrap in October 1924 to Stanlee, of Dover.