Near the end of episode 5 of Kantai Collection, Kaga said that a fleet of two aircraft carriers (Kaga and Zuikaku), two torpedo cruisers (Kitakami and Ooi), one battleship (Kongo) and one destroyer (Fubuki) was originally an impossible fleet, so they go along with assigning Fubuki - a destroyer - to be the flagship of the fleet.
Why is such a fleet an impossible one in the first place?
If you're willing to impose a certain level of realism on the show, then such a fleet would indeed be absurd by WWII-era naval warfare standards.
In WWII, the biggest source of firepower for a navy was large ships, primarily battleships and aircraft carriers. Such ships required a huge amount of resources to operate - Kaga, Zuikaku, and Kongou each had well over a thousand personnel on-board. They could be used effectively in a variety of situations, from naval combat, to blockades, to bombarding enemy troops anywhere near water.
But, such large ships had a fatal weakness, which had been known since the 19th century: torpedoes. A battleship could easily sink weak enemy boats from a long distance away. For example, Kongou's 356 mm guns had a maximum range of 35 km (the effective range was somewhat lower, but still quite far). However, if the enemy forces had a large number of small boats, each armed with torpedoes, it would be difficult for the battleship to take down all of these with its relatively slow weaponry. Certainly, it could hit some of them, but with enough numbers it wouldn't be able to take them all down effectively. Aircraft carriers fare a bit better in this respect, but they too had to worry about any sort of armored torpedo-carrying vessel or submarine, and enemy fire could prevent aircraft from launching or landing, which would basically cripple their offensive capabilities.
With enough ships, the enemy forces could easily advance to within the effective range of torpedo fire (which depended on the model of torpedo, but was around 4-8 km for one common torpedo used by the U.S. Navy). It would not take long to deal heavy damage to the large ship, possibly even sinking it. Small enemy vessels (such as cruisers) could also quickly approach to get in range of their own guns, at which point the main advantage of battleships and aircraft carriers (long range) is lost. If this seems like a poor strategy, keep in mind that torpedo boats could be very small (at some points even converted merchant/fishing vessels were used for this purpose), and operated by only a few people, yet a small number of them would pose a serious threat to much larger battleships and aircraft carriers. Thus, the big ships need some way to deal with smaller ships approaching them too quickly for the large ship to deal with.
This is the reason destroyers were invented. Destroyers were relatively heavily armored (given their small size), highly mobile small ships which were primarily used for short-range tactical combat and to escort larger ships. While torpedo-boats and other swarms of small ships could out-maneuver large ships with enough numbers, they weren't a threat if you could intercept them before they got in firing range and take them out. A destroyer like Fubuki would generally only be used in combat against other naval forces. Their medium-caliber guns could still easily outrange (maximum range of over 18 km) torpedoes, and would be a threat to approaching cruisers as well. A destroyer only required around 200 personnel, and more than just destroying enemy torpedo boats, they were generally pretty versatile: they could be used for holding tactical positions, reconnaissance, torpedoing enemy ships, attacking enemy submarines (essentially just underwater torpedo boats), and anti-air attacks, depending on the needs of the mission and the available equipment. Even in the worst case scenerio that the destroyer sinks, this still buys time for the (much more important) large ships to escape, fight back, or wait for reinforcements.
Generally, any larger ship during WWII would be escorted by at least one destroyer. Especially important ships might get more than one destroyer escort. So, for a fleet of 2 aircraft carriers, one battleship, and 2 light cruisers (Kitakami and Ooi are described as torpedo cruisers, but this is just a type of light cruiser armed primarily with torpedoes), we'd expect at least 5 or so destroyers, and possibly even more. For a real-life example, the Japanese fleet at the Battle of the Eastern Solomons had the following numbers, which were reasonably typical for a battle of this size:
A fleet of 2 carriers, 1 battleship, 2 cruisers, and 1 destroyer is rather absurd in comparison; it's putting far too many resources in the large ships, and not enough into protecting them. A swarm of small ships would pose big problems for a fleet like this. While such a fleet would have excellent offensive capability given the number of ships, they wouldn't have especially good defensive capabilities, and would be an attractive target for enemy attacks (basically a glass cannon).
In addition, the flagship was the most important ship in any operation. The commanding officer of the operation was on the flagship, and crippling or sinking the flagship would not only damage enemy morale, but also their communications and strategy. Making a ship that was designed to be relatively expendable, like a destroyer, would be a bad idea. The enemy forces would likely all target the destroyer, and the fleet would be in serious trouble if it sank, usually forced to retreat.
Typically, the flagship was one of the largest ships in any given operation, being difficult to sink, well-defended, and powerful enough to boost the morale of other ships in the operation. A small ship being the flagship would probably have problems with respect as well as being an easy target. While there were a couple cases where a destroyer was used as the flagship for an operation, these were generally only in cases that the whole fleet consisted of only destroyers, or when the original flagship was too heavily damaged to continue (such as in the Battle of Guadalcanal).
With all that said, none of this really applies very well to the Kancolle universe, at least in the game. Destroyers had a predominantly tactical, defensive role, but the game's battle system doesn't do much to emulate this. In game, most of the advantages of destroyers (evasion and speed) aren't particularly unique to them; one can replace destroyers with larger ships without much loss. This will incur larger ammunition and fuel costs, but it isn't necessarily a bad strategy or one that the enemy forces will have any way to exploit.
Indeed, once one progresses far enough in the game, even more unbalanced fleets become commonplace. Later missions require more and more firepower, which is increasingly hard to meet with weaker ships like destroyers and cruisers. The game is also generous enough with resources that the fuel and ammunition consumption become relatively unimportant. Since the number of ships you can bring to a battle is limited (as are your enemy's, preventing any kind of swarming strategy), it's often better for high-level missions to only deploy battleships and carriers. If you're well prepared, it's relatively rare that such large ships will take any serious damage, and with some strategy there's essentially no risk of them sinking. If anything, the single destroyer would be the weak link defensively, and unlike in the real world, where losing a single destroyer in an otherwise good battle would be seen as a big victory, in the game you can't afford to throw away experienced destroyers regularly.
Making the destroyer your flagship would offer it some protection, since in-game flagships can't be sunk, but if it reaches a heavily damaged level (which is quite plausible) you'll be forced to retreat. There are other benefits for the flagship, such as increased leveling and a chance to have attacks hit other ships instead. There are strategic benefits to both large and small ships being flagship, but in any case it's not crazy to make a weak ship like a destroyer the fleet's flagship.
I suspect there's no good in-universe reason to consider this strategy crazy or impossible, at least based on what we know now about battles in the Kancolle universe. In the game, it wouldn't really be at all, given the right circumstances. The anime hasn't presented us with any explanation, and it has an original story (since the game has almost no story), so we can't really find any answer there. But in the context of actual WWII-era naval battles, it would indeed be a crazy, illogical decision to make a fleet like this, and there are no historical examples of such a fleet.
I just checked the service record of each of those 6 named ships. And the end conclusion is that this was a double pun (sorta). They were deemed "impossible ships some ways or another". And they never served with each other...sorta?. Which makes the squadron utterly impossible.
On 12 January 1942, Chief of Staff Rear Admiral Matome Ugaki inspected Ōi, and expressed strong disapproval of the Navy's plans for the use of the newly remodeled torpedo cruisers and urged a revision to the Navy's tactics. While the Imperial Japanese Navy General Staff debated the issue, Ōi was assigned to escorting transports between Hiroshima and Mako, Pescadores Islands from the end of January through mid-April [1941].
The end result of which both becoming troop carriers and occasional attachment to patrols based around the Malaccas'. Rather uneventful career until Ooi was torpedoed off HK in 44. Kitakami survived and also was converted for Kaiten suicide operation which was also a botch.
I think they wanted to use Taihou instead of Zuikaku. Zuikaku was never an armored carrier (outside of Pearl Harbor 1941 which both, Zuikaku and Kaga, had participated with and hit different airfields from each other).
Zuikaku was remodeled (in-game) into an armored carrier, [Taihou, the only armored carrier of her class] blew up when exhaust gases...
Kaga was a part of an experimental program with Akagi, as the losing bet.
As a result, Akagi and Kaga were given different exhaust systems to evaluate in real-world conditions. Kaga's funnel gases were collected in a pair of long horizontal ducts which discharged at the rear of each side of the flight deck, in spite of predictions by a number of prominent naval architects that they would not keep the hot gases away from the flight deck. The predictions proved to be correct, not least because Kaga was slower than the Akagi which allowed the gases to rise and interfere with landing operations. Another drawback was that the heat of the gases made the crew's quarters located on the side of the ship by the funnels almost uninhabitable.
That and the impractical idea, that should she find herself in a duel with ships, she was equipped with ten 20 cm/50 3rd Year Type guns. On her second remodel she was modernized with more and better guns. This was before the realization that carriers were not meant at all for any gun duels.
Kaga was part of the 1st CV Div 1 and later the CV Div 2 from 1935 onward. Sunk 1942 Midway.
Zuikaku was part of CV Div 5 after returning from Pearl Harbor 1941. Served in Battle of Coral Sea in 1942 with Shoukaku around the same time Midway was happening.
Now this one was tough.
Under the 1922-1930 Washington Treaty, Japan was limited to certain tonnage/armaments limits and certain amounts of capital ships. Kongou exceeded both of those limits after her remodel from Nov 1929-March 1931 and was a full battleship. She should not exist according to the treaty that Japan wasn't due to renounce until 1934.
Met Zuikaku probably for Operation J as Kongou was mentioned to have escorted 5 fast carriers for capture of Java island (Feb-March 1942), which Zuikaku and Shoukaku later fought Battle of Coral Sea for Operation Mo (April 1942) in the same general area.
Escorted Hiryuu, Akagi, and Soryuu in Easter Sunday Raid, Ceylon April 1942, No Kaga.
Kongou met Zuikaku again June 1944 along with IJN Taihou. But then again like Pearl. This was a throw together of all mobile surface fleets. As taking the Mariana Isles would give US land based bombing range of Japanese home islands. Zuikaku and Taihou lost with all hands after being torpedoe'd by subs after battle.
Sunk Nov 16 1944 after being torpedoed while en route to Kure with remnants of 1st fleet. (Note the were in separate divisions commanded by a different rear admirals)
11th Destroy Div stationed around Hainan 1941, very active during Malaysia and Indonesia operations between Dec 1941 and her sinking on 11 Oct 1942. May have met any of the above ships for one operation or the other...Truly the mystery as why she would be included.
However she had been the black-sheep for the longest time for a friendly fire on Feb 29 1942 that saw a spread of torpedoes sinking 1 minesweeper and 3 troop ships, which was later attributed, post war, to the Mogami. Maybe that? I'm not sure how Japanese language can use the word impossible. But no doubt the captain refuted that some way or the other.
>> Call me cheap for using Wikipedia, but cross referencing this took around 2 and a half hours. With some conflicting sources that I had to double check via another source. No, I did not try to outdo the current upvoted. I just wanted to dig a bit deeper, see if there was any other reason why. I play this game, and the history does interest me. Whew, I lied when I said it would take 48, now that's 150 min wasted. BTW in KanColle game a fleet can only have 6 ships. And there's no objectionable reason why this couldn't happen, it wouldn't be very good but with some tweaking, maybe a powerful glass cannon.
