There's a scene in Star Trek II: The Wrath of Khan where the supposed uebermensch Khan is outmaneuvered by Capt. James Kirk in a space battle because Khan is moving his starship in a plane, neglecting the 3rd dimension. Kirk, veteran of hostilities of space, took advantage of this fact. Lousy excuse for an uebermensch aside, I couldn't help but think of that scene as I watched the first two episodes of Legend of the Galactic Heroes. (The first episode/movie was shown last year.) I was vastly amused to watch arrays of ships facing off against each other, moving in what was essentially a plane. I was also vastly amused (or frustrated) by the pathetic level of tactics displayed by both sides. Yes, splitting up your forces and looking at the world through rose-colored glasses is such a brilliant idea.
Puzzled by this seeming display of idiocy, I began thinking of possible reasons for the tactics depicted. And then I thought of reasons why those reasons didn't work too well...
1. The military ships on both sides don't have enough fuel to spare for fancy maneuvering and changing their velocity vectors. Even so, I would have thought that they might try to flank each other -- and in space, with its many degrees of freedom in movement, I would think "flanking" would be a matter of course. Heck, even the Greeks spent a good deal of time trying to outflank each others' troops, due to a peculiarity of the phalanx that left one side well-protected and the other exposed.
2. They mass their ships in clumps, instead of taking advantage of space, for defensive purposes. Alas, this one also doesn't make much sense. Those ships were packed pretty tightly from the looks of it, and I'd think you'd spread them out more to take advantage of angles-of-fire (not to mention reducing friendly fire casualties, etc.). For unlike land-based combat, where mass-of-troops is a factor, I can't see mass-of-ships as performing a similar function. Ramming ships into each other would likely be a last resort, if only because of economics. (Military hardware is expensive. If someone can explain to me how both sides fund their militaries, please let me know.) Trying to "corner" a fleet would be much, much more difficult than in two-dimensional combat; avenues of escape would be too many to fully cut off. All those ships don't do much good if you can't bring your weapons to bear on the enemy. Unlike the cavalry of old, the ships per se don't have shock combat value; their weapons do.
3. This point is mainly speculative, but why battle in the deeps of space? Are they in contested territory, well-patrolled by both sides? Interception fleets? You'd want to find a field (volume?) of battle favorable to your fleet disposition. But in open space, there are few such advantages to be found, and too many possibilities for stalemate. Depending on the circumstances, supply bases, libration points (the gravity well equivalent of "king of the hill," for those who don't know), and bases or planetary systems might make better battlesites. Without knowing the astrography and situations of the warring parties, though, this is difficult to judge.
4. Why are the officers on both sides so ridiculously useless? Actually, I can see this one happening. It's happened in the past, most commonly in military forces that have been at peace for a while. During such times, able administrators, paper-pushers, and politickers come to the fore, rather than the best strategists and tacticians. (Witness President Lincoln's search for a competent general in the American Civil War. You have to be pretty desperate to accept McClellan's bungling for long.) But they've been at war for the past 150 years. What gives? (Of course, the 100 Years' War between France and England was an on-and-off affair that lasted more like 150 years. So again, more background is needed.) Possibly relativistic factors result in admirals and captains living through fewer years than their ground-bound relatives and government, and thus the persistence of handicapping traditions. If this anime actually uses relativistic factors, I'll be impressed.
5. The above asinine tactics might be a result of straitlaced, traditional or stereotyped battle doctrines. (The neo-Prussian uniforms might be indicative...) Real-life example: doctrines through most of World War I, most notably the French offensive à outrance ("offense to the limit"). The American Civil War foreshadowed the advantages that newer weapons gave the defense, as well as the concept of total warfare, but save for a very few astute observers in Europe, everyone still subscribed to the Napoleonic doctrine of fast attack and decisive battles, not attrition. I haven't seen enough of the weapons systems to figure out what the offense-defense balance might be in Legend of the Galactic Heroes, but I suppose some such idiocy might persist.
6. Or maybe ages-old psychological factors are at work. After all, there is (an often politically influenced) tendency to proclaim swift, easy, and decisive victories through swift, easy, and decisive engagements. Long wars are expensive, unglamorous (once the patriotic notions of "dulce et decorum est pro patria mori" [roughly, "It is fitting and proper to die for one's country." -Ed.] have worn off), and generally unpopular. To use yet another American example, consider Vietnam. These commanders might be pursuing policies designed to gain them political support -- not necessarily compatible with sound tactical reasoning. Again, though, the time factor is a problem with this one. You'd think such commanders, after 150 years, would be weeded out by enemy fire.
7. Maybe the anime's creators are dumbing down the tactics so even absolute idiots can appreciate what's going on. If so, I'm underwhelmed. I'd rather see some intelligent battles, thanks. Of course, most of this may be premature. Maybe the battles improve. Maybe the idiots are removed from command. And maybe, just maybe, someone will actually think to move "up" or "down" or "diagonal" instead of in one plane.