 They fire 400 @-@ pound ( 181 kg ) projectiles using a 130 @-@ pound ( 59 kg ) gunpowder cartridge . Though they were insufficient against contemporary battleships , they were seen as adequate for the light cruisers that the fort was expected to face . The carriages weighed 13 long tons ( 13 t ) and moved on semi @-@ circular traverses . The guns were loaded either manually — using the <unk> ( <unk> ) system — or via the Armstrong mechanical <unk> . The Armstrong system enabled loading of the guns from behind the protection of the rampart whereas the manual system required at least two crew to be exposed on the rampart 's top . Despite this the guns were manually loaded for most of their operational life as the Armstrong cable drive was faulty and too difficult to maintain . The guns had a 14 @-@ man crew and loading took about 2 minutes , a rate of fire that was only slightly faster using the Armstrong equipment . 
