[1] The Edgars were protected cruisers, with an arched, armoured deck 5–3 inches (127–76 mm) thick at about waterline level.

[1][2] It contained four double-ended cylindrical Fairfields boilers feeding steam at 150 pounds per square inch (1,000 kPa) to 2 three-cylinder triple expansion engines,[3] which drove two shafts.

Endymion took part in suppressing the Boxer Rebellion in China, during which time future rear admiral and VC recipient Eric Gascoigne Robinson served aboard her.

Captain Alfred Paget was appointed in command in February 1901, and in December 1901 she visited Manila, where the Governor and US officers hosted the crew, including many with whom they had served together during the rebellion.

On 30 August 1918, she was damaged at Stavros, Greece by the Imperial German Navy submarine SM UC-37; her crew survived.