Sorry guys, I'm going to be a pain and pull you up here. You're talking about plunging fire with regard to pre-dreadnought battleships and I'm afraid you're way off base. At period battle ranges, plunging fire simply didn't happen - shooting over ranges of a few thousand yard meant flat trajectories for all guns. Angles of decent would be negligible, a few degrees at most, and shells simply could not hit decks or turret roofs at anything but the most oblique of angles. No decks or turret roofs were penetrated at either Yellow Sea or Tushima on either side. Not even once. Hell, even at the 10,000 - 18,000 yard ranges that Dreadnoughts fought over in WW1, the angle of descent was usually only about ten or fifteen degrees. Plunging fire was only just becoming a threat at the outer edge of the range envelope and even then no deck armour was penetrated at Jutland (a few turret roofs were, however).
Most dreadnoughts built before 1918 couldn't elevate their guns beyond 20 degrees. Few Pre-dreadnoughts could elevate their guns much beyond 10 degrees. Low elevation mounts like that simply could not lob shells on a trajectory that could actually generate plunging fire. It is only after WWI as battle ranges progressed out to 20,00 yards and beyond and most navies adopted 30 degree or more elevation mounts for their guns that plunging fire actually became a major threat to battleships.
rlbell, you also talk about pre-dreadnoughts being under armoured. Did you know that prior to the development of the first reliable fused APC shells by the Germans in 1911, battleships had great difficulty damaging one another at all? The Harvey and Krupp steel armour used on these ships was all but in-penetrable to equal calibre shells and 9" of Krupp steel was reckoned to enough to keep out 12" shellfire at anything but point blank range. In the Russo-Japanese war both navies had the option of either using solid shot that could just about defeat the best armour on the enemy ships but did little damage after that or common shell that was explosive but had effectively no armour piercing ability. At Yellow Sea, neither navy managed to do much meaningful damage to one another beyond wrecking the unarmoured (and unessential) upperworks of each other's ships with high explosives. The great damage inflicted on the Russian ships at Tushima had much to do with their poor condition after sailing halfway around the world and the parlous state of their crews (there seems to have been little to no attempt at damage control). In addition, the Borodino class ships that made up the core of the Russian fleet had a severe stability problem that caused them to capsize after taking on relatively little water.
Oh, by the way, Russian long ranged gunnery at Tushima was actually pretty good at first. The first salvo aimed at Togo's flagship fell only 20m short and the Mikasa was hit fifteen times in the first five minutes of the battle. The difference was that the Japanese guns had a higher rate of fire than the Russian guns and that the Japanese enjoyed a huge advantage in medium weight artillery. Also, initially they fired only common shell, seeking to start fires aboard the Russian ships and it was these uncontrolled fires that rendered most of them unable to fight effectively. The Japanese then switched to solid shot and used it to open up the sides of the damaged ships that fell out of line. Ultimately, the Russian ships lost at Tushima were disabled by high explosive fire but sank after taking on water through shell holes made around at the water line (most of them were overladen, so their armoured belts were submerged and offered no protection). None of the ships losses were attributable to deck hits as the battle was only fought at a range of about 7000 yards. Way too short for plunging fire.
Overall, aside from experiments with naval mortars in the Napoleonic period, plunging didn't really feature in naval gunnery at all until the latter part of WW1 and the post war period. Admittedly, thereafter it dominated gunnery theory and it wasn't long before deck protection was considered more important than belt protection, but in the Pre-dreadnought and early dreadnought era it just wasn't a factor.
