Arethusa 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.

On her commissioning she was assigned as the leader to the 2nd Destroyer Flotilla of the Harwich Force, guarding the eastern approaches to the English Channel.

Galatea was also the first to receive a hit by the German light cruiser SMS Elbing, but no explosion occurred.