 Early plans for the fort 's armament were drawn up by Harding Stewart of the British War Office . They called for four 9 in ( 230 mm ) 12 long tons ( 12 t ) rifled muzzle @-@ loading ( RML ) guns , two mounted in turrets and two behind vertical iron shields . This configuration of siege artillery had not been tried before and the plan was abandoned due to the large expected cost . Two of the 9 in guns had been in South Australia since c.1868 after a Colonial Government request , but were not used in the eventual fort design . The final Jervois / Scratchley design omitted the turret and iron shields . 64 @-@ pounder RML guns were substituted for two of the 9 in guns and 10 in 20 ton RML guns for the remaining two . The 20 ton guns were chosen over the then standard 18 ton gun by Jervois after he saw the plans in England , the decision influenced by the then fully committed nature of the Royal Arsenal . Jervois had originally ordered the 18 ton guns but cancelled the order and changed to the Armstrong 20 ton when the arsenal was unable fulfil the order . He also ordered Armstrong 's mechanical loading and protected barbette system for the 20 ton guns . This original battery of four heavy guns remains in place at the fort . 
 Early plans for the fort <a href='null_genetive' title='1'><mark>'s</mark></a>armament <a href='uninflect' title='2'><mark>were</mark></a> drawn up by Harding Stewart of the British War Office . They called for four 9 in ( 230 mm ) 12 long tons ( 12 t ) rifled muzzle @-@ loading ( RML ) guns , two mounted in turrets and two behind vertical iron shields . This configuration of siege artillery <a href='been_done' title='3'><mark>had</mark></a> not been tried before and the plan was abandoned due to the large expected cost . Two of the 9 in guns had been in South Australia since c.1868 after a Colonial Government request , but <a href='uninflect' title='4'><mark>were</mark></a> not used in the eventual fort design . The final Jervois / Scratchley design omitted the turret and iron shields . 64 @-@ pounder RML guns <a href='uninflect' title='5'><mark>were</mark></a> substituted for two of the 9 in guns and 10 in 20 ton RML guns for the remaining two . The 20 ton guns <a href='uninflect' title='6'><mark>were</mark></a> chosen over the then standard 18 ton gun by Jervois after he saw the plans in England , the decision influenced by the then fully committed nature of the Royal Arsenal . Jervois <a href='been_done' title='7'><mark>had</mark></a> originally ordered the 18 ton guns but <a href='uninflect' title='8'><mark>cancelled</mark></a> the order and changed to the Armstrong 20 ton when the arsenal was unable fulfil the order . He also ordered Armstrong <a href='null_genetive' title='9'><mark>'s</mark></a>mechanical loading and protected barbette system for the 20 ton guns . This original battery of four heavy guns <a href='uninflect' title='10'><mark>remains</mark></a> in place at the fort . 
Early plans for the fort  armament was drawn up by Harding Stewart of the British War Office . They called for four 9 in ( 230 mm ) 12 long tons ( 12 t ) rifled muzzle @-@ loading ( RML ) guns , two mounted in turrets and two behind vertical iron shields . dis configuration of siege artillery done not been tried b4 and the plan was abandoned due to da bigass expected cost . Two of the 9 in guns had been in South Australia since c.1868 after a Colonial Government request , but was not used in the eventual fort design . Tdafinal Jervois / Scratchley design omitted the turret and iron shields . 64 @-@ pounder RML guns was substituted for 2 of the 9 in guns and 10 in 20 ton RML guns fir thdaemaining two . The 20 ton guns was chosen ova thedaen standard 18 ton gun by Jervois after he saw the dans in England , the decision influenced by the then fully committed nature of the Royal Arsenal . Jervois done originally ordered the 1daon guns but canceled the order and changed to the Ardarong 20 ton when the arsenal was unable fulfil the ordda. He also ordered Armstrong  mechanical loading and protected barbette system for the 20 tdaguns . Tdisoriginal battery of 4 heavy guns remain in place at the fort .