"Shannon" displaced as built and at deep load. The ship had an overall length of , a beam of and a mean draught of . Her beam was wider and her draught one foot less than her sisters in the belief that she would prove to be the fastest ship in the class. "Shannon" was powered by a pair of four-cylinder triple-expansion steam engines, each driving one shaft, using steam provided by 24 Yarrow water-tube boilers. The engines were designed to reach a total of and were intended to give a maximum speed of . "Shannon" proved to be the slowest ship in the class; during her sea trials on 3 December 1907 her engines reached , but she only reached a speed of The ship carried a maximum of of coal and an additional of fuel oil that was sprayed on the coal to increase its burn rate. At full capacity, she could steam for at a speed of . "Shannon" was designed to carry 779 officers and enlisted men, but had a complement of 819 in 1908 and 842 in 1912.