The ship was converted to operate a mix of wheeled aircraft from her forward flying-off deck and floatplanes that were lowered into the water.

Pegasus spent the last year of the war supporting the Grand Fleet in the North Sea, but saw no combat.

On sea trials in December 1914, Pegasus made 9,722 shp (7,250 kW) and reached 20.8 knots (38.5 km/h; 23.9 mph).

She carried 350 long tons (356 t) of oil which meant that she could steam for 1,220 nautical miles (2,260 km; 1,400 mi) at her maximum speed.

[4] HMS Pegasus was fitted with a flying-off deck forward, intended for aircraft with wheeled undercarriages, and a prominent hangar aft.

The smaller forward hangar was built under the ship's bridge and the aircraft were raised to the flight deck overhead by one of the first lifts in the Royal Navy.

She participated in a few uneventful operations in the North Sea, but was mostly occupied with pilot training and ferrying aircraft to ships equipped with flying-off platforms.

Pegasus supported the British intervention in the Russian Civil War between May and September 1919 and was based at Archangel.