The ship had an overall length of , a beam of , and a draught of at deep load. She displaced . Her two direct-drive steam turbines, each driving a propeller shaft, were designed to produce a total of and a speed of . On sea trials in December 1914, "Pegasus" made and reached . The ship was converted from coal to fuel oil at the suggestion of her builders. She carried of oil which meant that she could steam for at her maximum speed. Her crew numbered 258, including 100 aviation personnel.