 The ship was used as a target to test the effect of various weapons on capital ships , along with Emperor of India . The tests included firing destroyer armament at the upper works at close range to test their effectiveness in a simulated night engagement , direct hits from 13 @.@ 5 @-@ inch shells , bomb tests , and experiments with flash tightness in the magazines . The first two tests were conducted in July 1931 , and were <unk> of magazine explosions . The <unk> system worked as designed , and while the explosions caused serious internal damage , Marlborough was not destroyed , as the three battlecruisers had been at Jutland . In 1932 , further tests were conducted with <unk> 250 @-@ pound ( 110 kg ) and 500 @-@ pound ( 230 kg ) bombs to test deck strength ; 450 @-@ pound ( 200 kg ) armour @-@ piercing ( AP ) bombs and 1 @,@ <unk> @-@ pound ( 490 kg ) high explosive ( <unk> ) bombs were then detonated inside the ship to test their effectiveness . The Royal Navy determined that the <unk> bombs were useless , but that thick deck armour would be required to defeat AP bombs . This led to the decision to reinforce the deck armour of existing battleships throughout the 1930s . 
