Alternate universes and parallel words are full of weird warships. But reality is sometimes even more weird than fantasy.
One of the most popular althistoric concepts is the big-gun aircraft carrier. Such ships look good on paper or forum board: big enough to carry a heavy gun battery and substantial air wing, well-protected against enemy shelling and torpedo attacks, fast and furious. Besides, let's not forget about close relation between battleships and aircraft carriers (HMS Eagle, Japanese Kaga and French Bearn were converted super-dreadnoughts) and numerous efforts to provide carriers with serious armament (USS Lexington and Saratoga initially carried a heavy cruiser battery, 4 × twin 8-inch guns).
Althistoric battleships/carriers usually have two forward-looking turrets. But what about a real battleship-carrier with four turrets, spacious flying deck and a wing of no less than 22 aircraft? They were real, an emergency class of two hybrid ships induced by severe lack of carriers during WWII.
Ise and Hyūga, originally planned as the third and fourth battleships of the Fusō' class, started their life in 1917-1918 as super-dreadnoughts, armed with an impressive battery of twelve 14-inch guns in twin turrets. Both were extensively modernized in late 1930s - just to be rebuilt five years after.
Here's the story of their conversion, told by Stuart Slade:
"The Japanese studied conversion schemes for all ten of their older battleships after Midway. Initially, these were full-scale jobs, involving removing all superstructure, main batteries and heavy/secondary guns then adding a full-length flight deck, island superstructures, offset funnels and AA batteries. Airgroup was estimated at 54.
"The Kongo's were ruled out because they were the only big-gun ships fast enough to act as carrier escorts, the Nagato's because the IJN did not want to lose their 16 inch guns. Eventually surveys showed that rebuilding the remaining four battleships was not viable; the conversions would take at least two years and would consume more resources than building carriers from scratch.
Battleship/carrier Ise, August 1943
"That left the idea of rebuilding the four 14 inch ships as semi-carriers. Originally, it was planned to rebuild all four ships (they were very unsatisfactory battleships; the distribution of turrets along the ship's length gave an awful lot of magazines to hit and the 1930s rebuilds had been carried out without proper structural analysis causing excessive stress). However, shipyard congestion meant that only two battleships could be converted, so the Fusō's were dropped from the program.
"The reasons for the selection of the more modern Hyūga's for the conversion were mostly gunnery. The Japanese had increased the elevation of the ship's guns by deepening the gunwells in the turret rather than raising the trunnions. Hull depth aft had prevented this for the aftermost turrets so they had severely restricted elevation, at long range reducing the gunpower of the ships by a third. Also, Hyūga had had a turret explosion on 15 May 1942 that had destroyed X turret - damage that still had not been repaired. Although Ise and Hyūga were slightly faster than their older cousins, the difference was not enough to be really significant.
Artist's impression of the battleship Hyūga after conversion
"There were a lot of competing plans for the conversions, including some that would have removed four turrets rather than two. In fact, the simplest and least extensive was chosen. Analysis showed that the ships could only use one catapult at a time so any airgroup larger than 24 aircraft could not be efficiently launched.
"The conversion saw the removal of both aft turrets (weighing 864 tons each) and both barbettes (another 800 tons). In their book, Layman and McLaughlin claim that the hangar deck/flight deck/catapult assembly weighed much less than this, leading to a dangerous increase in metacentric height with the resultant danger of very rapid rolling. This, they indicate was the reason why the aircraft deck was covered with an 8 inch layer of concrete, reducing the weight loss to 600 tons.
"Personally, I would argue this. I believe that the concrete was put in there to correct a trim problem - the nearly 2500 tons lost was at the end of the ship's moment arm while the flight deck was weight distributed over a significant proportion of the ship's length. Shifting weights around like this is no small matter - even apparently small changes in weight distribution can have unpleasant and unanticipated side-effects. My guess is that, without the concrete additions, the ship would have trimmed badly by the bows with a very serious impact on speed.
"The concrete would also have stiffened the ship aft, replacing some of the structural support lost by removing the barbettes. All four Japanese 14 inch battleships were structurally weak, anyway, so reinforcement would have been no bad thing. "
Battleship Ise underway at Leyte Gulf 1944
So, the ships retained four of their six turrets. With 44 aircraft, they were supposed to be a serious reinforcement for Kaigun (Imperial Japanese Navy). Actually, none of them played a critical role in 1943-1945 naval battles. Both were lucky enough to survive aerial bombardments, mines and close pursuit by submarines but on the last stage of war Ise and Hyūga were stationed at Kure, with no fuel or aircraft. One was struck by bombs dropped by the US Navy Corsair planes, the other was run aground by her crew.
Bottom line (for althistorians only): if you need a battleship, build one. The same rule applies to carriers. Any crossbreed between them will result in a ship inferior to "proper" dreadnoughts and flat-tops. So don't even try it - except if you're designing a ship for your enemy.