The closing gear and lever were part of one of the guns that made up the armament of HMAS Australia (1913-1924). HMAS Australia was an Indefatigable Battle Cruiser built by John Brown & Co Ltd in Scotland and was launched in 1911. Australia was commissioned at Portsmouth in 1913 and sailed to Sydney as Flagship and lead the newly formed Australian Fleet Unit into Port Jackson for the first time. When World War 1 broke out HMAS Australia was assigned the role of operating as counter to the German Pacific Squadron and was employed in the Pacific till the next year. Late 1914 saw Australia sail to England to become the Flagship of the 2nd Battle Cruiser Squadron and patrol the North Sea for four years. In 1918 HMAS Australia was used for experiments with aircraft which were successfully launched from a platform erected on one of her gun turrets. After the surrender of the German fleet Australia returned to Sydney and was decommissioned in December 1921 and then sunk along with her armament in 1924.
(http://www.navy.gov.au/spc/history/ships/australia.htm)
HMAS Australia was launched in 1911 by Lady Reid, wife of Sir George Reid (former Prime Minister), with an armament compliment of 8 12 inch guns, 14 4 inch guns and 2 18 inch torpedo tubes. This gear and lever are from one of these guns and were salvaged by someone before the ship was sunk in 1924.