Well, it got stopped by something. There is a similar picture floating around (can’t remember the name so I can’t find it now) of an imprint on a DD (ergo, no armor) that punched on through. It killed everyone in that boiler room and stunned everyone in the adjacent boiler room. Didn’t sink the ship, though.
There was some debate about whether it was a two-engine plane so maybe it was bigger but only the fuselage went in.
To me those big round things on the heavy cruiser photo look to be 3 foot diameter rivets used to hold on an armor plate. Not sure what else they would be.
Blanked-over portholes, I’m guessing. Even Yamato didn’t use 3-foot rivets to hold on the armor plate. 
And Sussex was in the London sub-class of the County class, not Kent. I’m looking for better pix or a source to see how high the armor belt might have gone.
DesertDog, I stand corrected, she was a London class. They had no armor belt, except for HMS London, after her rebuild.
One basic rule: “A ship captain should never put his ship and men in any kind of unnecessary danger.”
In war, one sticks to what’s safe and easy, as long as possible. Having said that, Battleships were rarely committed in a near-suicidal manner with little chance of surviving, even if they could theoretically accomplish the mission. The only exception I can think of was the Yamato and those at Leyte Gulf. And for both sides, Leyte Gulf was a rare example of a battleship-centered operation, made more amazing since it happened late in the war. The Japanese couldn’t afford to lose the Philippines, their carrier force was shot, and all they had left were battleships. Halsey for the Americans had an overwhelming advantage in air power but thought 15 carriers with 1,200 panes (nearly half of them fighters) might prove iffy against 7 battleships coming at you. So he wanted his four South Dakotas and two Iowas to take center stage if it came to it. In hindsight, it took more than 200 attack planes to sink either the Yamato or the Musashi, so Halsey may have been right. Only trouble was the Japanese had his number and knew his likely strategem.