 The main deck armor consisted of three layers of high @-@ tensile steel ( HTS ) 69 mm ( 2 @.@ 7 in ) thick that connected to the top of the upper strake of side armor . The flat portion of the lower deck had one layer of Ducol steel 25 mm thick with two layers of HTS of equal thickness above it . About 3 meters ( 9 ft 10 in ) from the side of the hull , this deck , now composed of three layers of HTS , totaling 75 mm ( 3 in ) in thickness , sloped downwards where it met a short horizontal armored ( three layers of HTS with a total thickness of 66 mm ( 3 in ) ) deck that connected to the main armored belt and the torpedo bulkhead . This was also made up of three 25 mm layers of HTS and curved up and outwards to meet the short horizontal armored deck . It enclosed a water @-@ tight compartment that was 3 @.@ 05 meters ( 10 ft 0 in ) from the side of the ship . It was backed by fuel oil tanks 3 @.@ 13 meters ( 10 ft 3 in ) deep . The outermost void was designed to allow the explosive force of a torpedo 's warhead to dissipate as much as possible while the oil tank was supposed to stop any fragments from penetrating the innermost bulkhead protecting the ship 's vital areas . 
