Officially reported by the Australian Naval Representative in London as being "anxious to command a ship of the RAN" and "in entire sympathy with the Australian Navy movement", he was given command of a new light cruiser, the Town class HMAS Sydney (1912), in June 1913; he had held the RAN rank of captain since March.

In the First World War, Glossop commanded Sydney during the 9 November 1914 Battle of Cocos, defeating the German light cruiser SMS Emden in a one-on-one engagement and forcing her to ground herself.

On 9 February 1917, he was relieved by Captain JS Dumaresq and sailed for Australia to take up the three-year appointment of Captain-in-Charge of Naval Establishments, Sydney.

Glossop was promoted to commodore 2nd class on 1 March 1919 and in June presided over the controversial court-martial of mutineers of HMAS Australia.

He reverted to the RN in October 1920, and after a short period as coast guard captain at Queenstown, Ireland, was promoted rear admiral on 20 November 1921 and retired next day.