Post-war Agamemnon was part of the British squadron that went to Constantinople in November 1918 following the armistice. She returned to the United Kingdom in March 1919, where she paid off at Chatham Dockyard and went into reserve on 20 March. In September 1918, the Commander-in-Chief, Grand Fleet, Admiral David Beatty, had called for a large target to be provided which would allow realistic gunnery practice for the battleships of the Grand Fleet, which had seen little action since the Battle of Jutland in 1916. Tests against armour plate in 1919 demonstrated that firing 15-inch (381-mm) guns at any pre-dreadnought would sink her quickly, but the use of a pre-dreadnought for target practice and tests by guns of 6-inch calibre (152-mm) or smaller seemed practical. At first, the pre-dreadnought was suggested for target duties, but ultimately Agamemnon became available and was selected instead. Based on the earlier experience in Radio Control British drone weapons 'Agamemnon' was modified at Chatham Dockyard for use as a target ship between 6 December 1920 and 8 April 1921. The ship was rewired for radio control and stripped; the 12-inch turrets remained aboard, but all of her guns and their equipment were removed, as were her torpedo equipment, flying deck, sea cabins, main derrick and boat equipment, lower conning tower, masts and yards, most of her crew amenities, and other unnecessary equipment. Unnecessary hatches, coamings, scuttles, and lifts were removed and plated over, and she was ballasted differently than she had been as a battleship. It was not intended to sink her, so she was assigned a crew of 153 to maintain and operate her when she was not under fire. Agamemnons first target service took place before her modifications were completed. On 19 March 1921, she was exposed to a cloud of poisonous gas to determine the effect of gas on a battleship. It was found that gas could penetrate the ship via her various openings, but the ship had not been sealed against gas before the trial and no accurate results applicable to a commissioned battleship could be obtained. On 21 September, she was subjected to machine-gun fire by strafing aircraft. These trials showed that such strafing could harass a battleship, but could not impair her fighting or steaming capabilities, and helped to determine protection for bridge personnel. Agamemnon also was used to test the vulnerability of battleships to 6-inch (152-mm), 5.5-inch (140-mm),