 Sometime after Koldun was completed , an armored ring , 5 inches ( 127 mm ) thick and 15 inches ( 381 mm ) tall , was fitted around the base of the turret to prevent splinters from jamming it . Later , an armored , outward @-@ curving bulwark was fitted around the top of the turret to protect any crewmen there . Three sponsons were later added , probably during the 1870s , to the upper portion of the turret . Each sponson , one above the gun ports and one on each side of the turret , mounted a light gun , probably a 1 @.@ 75 @-@ inch ( 44 mm ) Engstrem gun , for defense against torpedo boats . A fourth gun was mounted on a platform aft of the funnel when a hurricane deck was built between the funnel and the turret , also probably during the 1870s . 
