 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 Hibernia was suggested for target duties , but ultimately Agamemnon became available and was selected instead . 
