 Vanguard 's underwater protection was enhanced when she was redesigned in 1942 to reflect the lessons learned when Prince of Wales was sunk by Japanese torpedo bombers . It still consisted of a three @-@ layer system of voids and liquid @-@ filled compartments meant to absorb the energy of an underwater explosion . It was bounded on the inside by the 1 @.@ 75 – 1 @.@ 5 @-@ inch ( 44 – 38 mm ) torpedo bulkhead . Her enlarged oil tanks reduced the empty spaces that could flood and cause the ship to list and greater provision was made to pump these spaces out . The longitudinal bulkheads of the side protection system were raised one deck higher to further subdivide the spaces behind the waterline armour belt . The side protection system had a maximum depth of 15 feet ( 4 @.@ 6 m ) , but this decreased significantly as the ship narrowed at its ends . Over the length of the citadel , this system was found to be proof against 1 @,@ 000 pounds ( 450 kg ) of TNT during full @-@ scale trials . 
